1. TYPES, BIOLOGYANDFEATURES OF VECTORS
Chapter two

2. 1. What will be the consequence of not having an origin of replication (ori)in the vector?
A. If an ori is absent, replication of vector would not take place
B. As the cells divide after taking up the vector, both the daughter cells would be
having the vector
C. A colony of transformed colonies is observed
D. The vector won’t be taken up by the cell

3. Answer: a Explanation:
In the case ori is absent, the vector won’t be able to replicate. As the
replication won’t take place, only one of the daughter cells would be having
the vector. A colony of transformed colonies won’t be obtained. The puc18 ori
came from a plasmid in clinical bacterial isolate and was called as pMB1.

4. 2. It is requiredto distinguish between the cells that have taken up the vector
and that have not. It is done by using __________
A. multiple cloning site
B. origin of replication
C. high copy number
D. selectable marker

5. 7. If a plasmid is having two antibiotic resistant genes, say ampicillin resistant and
chloramphenicol resistant. If the plasmid grows in ampicillin containing medium
but not in chloramphenicol, what can be concluded?
A. The insert is not present in any of the gene
B. The insert is present in ampicillin gene but not in chloramphenicol gene
C. The insert is present in choramphenicol gene but not in ampicillin gene
D. The insert is present between both of the genes

6. 4. If you clone a DNA fragments by using vector Pbr322at multiplecloning sites of TcRgene
on the picture, one of the following is not true about successfully transformed clone?
A. Successfully transformed are tetracycline resistant
B. Successfully transformed are tetracycline sensitive
C. Successfully transformed are ampicillin resistant
D. Successfully transformed can survive on plate containing ampicillin

7.  DNA molecule used for carrying an exogenous DNA into a host organism and facilitates
stable integration and replication inside the host system
Genetic vectors are vehicles for delivering foreign DNA into recipient cells.
 In molecular cloning, a vector is a DNA molecule used as a vehicle to artificially carry
foreigngeneticmaterial into another cell, where it can be replicatedand/or expressed.
 Vectors can replicate autonomously and
 Typically include features to facilitate the manipulation of DNA as well as a genetic
marker for their selective recognition.
Vectors

8. Vectors can be classified as:
1. Cloning vector
2. Expression vector
Apart from the following, there is another class of vectors known as shuttle vector
Cloning Vector
 Vector used for replication of a cloned DNA fragment in a host cell.
 Engineered to contain “ori” – origin of replication sites
 Examples of commonly used cloning vectors are: pUC18, pUC19, pBlue script vectors
etc

9.  Stability in host cell
 Ability to control their own replication
 Small size (make transformation easy)
 Multiple cloning sites (MCS)
 Should not be transferred by conjugation
(prevents recombinant DNA to escape)
 Selectable marker gene
Important features of a cloning vector

10.  The different types of vectors available for cloning are:
 Plasmids
 Bacteriophages
 Bacterial Artificial Chromosomes (BACs),
 Yeast Artificial Chromosomes (YACs) and
 MammalianArtificial Chromosomes (MACs).
 The cloning vectors are limited to the size of insert that they can carry. The suitable
vector for a particular purpose is selected depending on the size and the application of
theinsert
Types of Cloning Vectors

11.  Cloning vectors extensively used in molecular cloning experiments can be considered
under following types: plasmid, phage vector and cosmid.

13.  Naturally occurring extra chromosomal ds circular DNA molecules
 Can autonomously replicate inside bacterial cells.
 Range in size from about 5.0 kb to over 400 kb.
 They encode only few proteins required for their own replication
 Only a small region surrounding the ori site is required for replication
 The host range of a plasmid is determined by its ori region
 Ex. plasmids with Col E1 ori - replicate in enteric bacteria, such as E. coli,
Salmonella
Plasmids

14.  Plasmids are inserted into bacterial cells by a process called transformation.
 Plasmids can accommodate an insert size of up to 15 kb DNA fragment.
 Generally, plasmid vectors carry a marker gene which is mostly a gene for antibiotic
resistance; thereby making any cell that contains the plasmid will grow in presence of
the selectable corresponding antibiotic supplied in the media.

15. Some of the phenotypes which the naturally occurring plasmids
confer on their host cells:
• Antibiotic resistance
• Antibiotic production
• Degradation of aromatic compounds
• Haemolysin production
• Sugar fermentation
• Enterotoxin production
• Heavy metal resistance
• Induction of plant tumors
• Hydrogen sulphide production

16.  Most plasmids exist as double stranded circular DNA molecules
 Linear plasmids have been found in a variety of bacteria,
 e.g. Streptomyces sp. and Borrelia burgdorferi
 Few types of plasmids are also able to replicate by integrating into bacterial chromosomal
DNA;
 These are known as integrative plasmids or episomes
 In prokaryotes they are found in Escherichia coli, Pseudomonas species,
Agrobacterium species etc.
 In eukaryotes they are mainly found in Saccharomyces cerevisiae.

17. Divided into 6 major classes depending on their phenotype
1. Resistanceor R-plasmids
• Carry genes which give resistance to the bacteria from one or more chemical agents, such
as antibacterial agents
• Very important in clinical microbiology Eg: RP4 plasmid, which is commonly found in
Pseudomonas and in many other bacteria
2. Fertility or F-plasmids
• Are conjugative plasmid found in F+ bacterium with higher frequency of conjugation.
• Carries transfer gene (tra) and has the ability to form Conjugation Bridge (F pilus) with
F- bacterium. Eg: F plasmid of E. coli.
Types of Plasmids

18. 3. Col plasmids
• Have genes that code for colicins, proteins that kill other bacteria. Eg: ColE1 of E. coli.
4. Degradative plasmids
• Allow the host bacterium to metabolize unusual molecules such as toluene and salicylic
acid. Eg TOL of Pseudomonas putida.
5. Virulence plasmids
• Confer pathogenicity on the host bacterium. Eg: Ti plasmids of Agrobacterium
tumefaciens, which induce crown gall disease on dicotyledonous plants.

19.  Based on the origin or source of plasmids, they have been divided into two major
classes:
 As natural and artificial
6. CrypticPlasmids
 Do not have any apparent effect on the phenotype of the cell harboring them.
 They just code for enzymes required for their replication and maintenance in the host cell

20. 1. RSF1010
 Isolated from E. coli K-12.
 This plasmid has broad hostrange in gram negative bacteria.
 The size of plasmid is 8694bp.
 Antibiotic resistance genes for Streptomycin and sulfonamides have present.
 Has either bi- or uni-directional replication from unique ori-V region.
 It cannot initiate transformation independently but can be transferred to host bacterium
in presence of helper plasmid.
Natural Plasmids

21. ColE1:
 Multi-copy plasmid obtained from E.coli (copy number is around 40).
 Size of plasmid is 6646bp.
 It forms the basis of manyartificial vectors used in molecular cloning.
 Has genes for colicin E1 production. Colicin is an antibacterial toxin produced under
stressed condition. Cells harboring the plasmid will have resistance against the toxin.
 For using in molecular cloning experiment, colicin genes are replaced with selection
marker (antibiotic resistant) gene.

22. Naturally occurring plasmids has several limitations; for example,
 some are stringent and not relaxed (pSC101),
 some has poor marker genes (ColE1), and
 some are too large (RSF2124).
To overcome the limitations of natural vectors, artificial plasmid are designed by combining
different elements from diverse sources
Artificial Plasmids

23. Artificial plasmids vectors can be used as:
1. Cloning vector
2. Expression vector
Apart from the following, there is another class of vectors known as shuttle vector
Examples of plasmids as Cloning Vector
 A widely-used E. coli cloning vector
 The p = "plasmid" and
 BR = "Bolivar" and "Rodriguez", researchers who
constructed it.
1. pBR322

24.  It is 4361 base pairs in length. Has the following
elements:
 “rep” site for replication of the plasmid (pMB1)
 “rop” gene encoding Rop protein
 “tet” gene encoding tetracycline resistance (pSC101)
 “bla” gene encoding ampicillin resistance
(transposon Tn3)

25.  pUC plasmids are small plasmids (2686bp)
 The p = plasmid and UC = University of California.
 pUC vectors contain a lacZ sequence and multiple cloning site (MCS)
 pUC18 and pUC19 vectors are identical (MCS is arranged in opposite orientation)
Advantage over pBR322:
 Very high copy number (500-700)
 Due to mutation on ori site
 Needs single plating for selection
 LacZ based
 Possible to insert gene having two different sticky ends using MCS
2. pUC plasmids

26. pUC vectors consists of following elements:
 pMB1 “rep” replicon region
 “bla” gene encoding ampicillin resistance
 E.coli lac operon system
 “rop” gene is removed from this vector which
leads to an increase in copy number.
Q. What is the importance of having MCS over
single restriction site?

27. PHAGES, COSMIDS, FOSMIDS, PHAGMIDSAND ARTIFICIALCHROMOSOMES
 To insert DNA fragments of more than 10 kb, normally plasmids are not the suitable
vehicles, as large inserts may trigger plasmid rearrangement or affect plasmid
replication
 This leads to development of a new class of vectors based on bacteriophages and Hybrids
vectors
 This create a capacity to load larger insertsize and higher transfectionefficiency

28.  The viruses that infect bacteria are called bacteriophage.
 These are intracellular obligate parasites that multiply inside bacterial cell by making use of
some or all of the host enzymes.
 Bacteriophages have a very high significant mechanism for delivering its genome into
bacterial cell. Hence it can be used as a cloning vector to deliver larger DNA segments.
 Most of the bacteriophage genome is non-essential and can be replaced with foreign DNA.
 Using bacteriophage as a vector, a DNA fragment of size up to 20 kb can be transformed.
A. Phage Vectors

29.  Amongst various bacteriophages available such as λ, T4, T5, and T7 phages; the λ phage
gained favorable attentiondue to its unique life cycle
λ phage:
 Bacteriophage λ contains ~49kb of DNA and
 Has a very efficient mechanism for delivering its genome into a bacterium.
Two key features
 One-third λ genome is non-essential
 Packing of DNA in phage could only take place if the size is between 40 and 52 kb long, a
constraint that can be used to ensure packaging.

30. Two problems had to be addressed before λ -basedcloning vectors couldbe
developed:
 Packaging problemwt size limitation of the insert DNA, Hence λ vector should be
smaller in size than wild type λ genome
 Bacterial restrictiondigestionsystem may target the modified vector. This limitation
can be overcome by replacing or mutating the restriction sites

31. Two types of vector have been developed using λ
genome
 Foreign DNA sequence is inserted into the λ
genome without any significant change of the
wild type genome.
 Smaller insert size (up to ~10kb).
 They may contain a multiple cloning site inserted
in lacZ system for screening of recombinant
bacterial colonies.
 Can be used to clone smaller DNA molecule.
 Eg: λ ZAP, λ gt
1. Insertion vectors:

32.  Full length λ molecule having two identical
restriction sites flanked by “stuffer fragment”.
 Stuffer fragment is replaced by foreign DNA
during restriction cloning.
 The vector without the foreign insert cannot
be packaged
 Due to the size limitation (smaller than the
required).
 Insert size ranges between 10-23 kb.
 Example: λ EMBL 3, λ EMBL 4, λ DASH.
Replacement vectors:

33.  The λ genome is linear, but in the ends has 12-nucleotides overhangs, termed as cos sites
 can be circularized using cos site which can be manipulated and replicated inside E. coli
 A more efficient uptake system called in vitropackaging can be utilized:
 left arm-new DNA-right arm + in vitro packaging mix
 phages are co-incubated with E. coli cells, and
 the infection process naturally transports the vector plus new DNA into the bacteria
 bacterial lysis forms a zone of clearing, called a plaque
Features of λ Phage Vectors

34.  M13 phage is filamentous phage that infects E. coli via F-pilus. The genome is a single
stranded circular DNA of size ~6.4kb surrounded by a proteinaceous coat
M13 Phage Vectors

35.  After entering to E. coli host, plus (+) strand converts into double stranded
DNA molecule called replicative form(RF)
 M13 vectorshave useful application in:
 DNA sequencing
 Mutagenesis study
 Probe generation
 Phage display
 Displaying proteins on the phage particle

36.  First described by Collins and Hohn in 1978,
 A type of hybrid plasmid with a bacterial “ori” sequence and a “cos” sequences
derived from the λ phage.
 Cos site required to be recognized as a „λ genome‟ by the proteins that package
DNA
 Once inside the cell it will replicates as a plasmid
 Recombinant DNA is therefore obtained from colonies rather than plaques.
 They frequently contain a gene for selection such as antibiotic resistance.
 They are able to load 37 to 52 kb of DNA, while normal plasmids are able to carry
only 1–26 kb.
 Sometimes helper phage is used to assist in packaging
B. Cosmid

37. Cosmids are widely exploited to build genomic libraries

38.  Slower replication
 Higher frequency of recombination inside bacterial
host.
 Unstable inside E. coli host and thus easy to lose vector.
Example:
 pJB8 is 5.4 kb in size and carries the ampicillin-
resistance gene (ampR),
 a segment of λ DNA containing the cos site, and an E.
coli origin of replication (ori).
Limitation of Cosmidvector

39.  Fosmids are similar to cosmids, however they are primarily based on bacterial F- plasmid.
 Developed by Simon and co-workers, in 1992
 They carry the F plasmid origin of replication and a λ cos site.
 can carry up to 40 kb of insert DNA.
 E. coli host can only contain one fosmid molecule- that offers higher stability as compared
to high copy number cosmids
 Fosmids have high structural stability and have been found to maintain human DNA
effectively even after 100 generations of growth
C. Fosmid

40. Fosmids contain several functional elements
 OriT (Origin of Transfer)
 OriV (Origin of Replication)
 tra-region (transfer genes)
 IS (Insertion Elements)

41.  M13 vectors has a limit to the size of DNA fragment that can be cloned
 To overcome this limitation, phagemid vectors were developed by combining a part of
the M13 genome withplasmid DNA
 Developed as a hybrid of the filamentous phage M13 and plasmids
 Can get packed as a phage particle but also can propagate as a plasmid
 Origin of replication (ori) for double stranded replication inside E. coli host, as well as
an “f1 ori” to enable single stranded replication and packaging into phage particles.
 Generally encode no or only one of the capsid proteins, the rest provided by the helper
phage
D. Phagemid

42. The components present in a phagemid vector are:
 Origin of replication (ori) of a plasmid.
 Intergenic region (IG region) which contains the packaging signal for the phage particle and
also has replication origin inside phage.
 A gene encoding phage coat protein.
 A selection marker.
 Restriction enzyme recognition sites.
 are commonly used for “phage display technology”
 double stranded phagemid vectors can be converted into single stranded vectors and
 packaged into virion particles by infecting the cells with helper phage

43. Phagemid has certain advantages over phage
vectors:
 The carrying capacity is higher than phage
vectors.
 has higher efficiency in transformation
than phage vectors.
 are genetically more stable than
recombinant phage vectors.

44.  Can be exploited to generate ss DNA template for sequencing purposes.
 Ss phagemid vectors inside the phage can be targeted for site-directed mutagenesis.
 Ss vectors can be used to generate hybridization probes for mRNA or cDNA.
Examples of Phagemid
1. pEMBL
 One of the first hybrid phagmid vectors constructed in 1983.
 They are characterized by the presence of:
I. The bla gene as selectable marker for ampicillin resistance.
II. A short segment coding for the alpha-peptide of beta-galactosidase (lacZ) and
III. Containing a MCS.
 The intragenic (IG) region of phage F1 have been used successfully for DNA
sequencing with the dideoxy method

45. Compared to M13 vectors
 pEMBL plasmids are smaller in size
 Purification of DNA is simpler.
 In addition, long inserts have a higher
stability in pEMBL plasmids than M13
vectors

46. Are DNA molecules assembled in vitro from defined constituents that can function likenatural
chromosomes.
Types of artificial chromosomes
 Bacterial artificial chromosomes (BACs) are simple plasmid which is designed to clone very
large DNA fragments ranging in size from 75 to 300 kb in E.coli host
 BACs basically have marker like sights such as antibiotic resistance genes and a very stable
origin of replication (ori) that promotes the distribution of plasmid after bacterial cell division
and maintaining the plasmid copy number to one or two per cell.
E. Artificial Chromosomes
1. Bacterial Artificial Chromosomes: BAC

47. Common gene componentsare:
1. oriS, repE – F for plasmid replication and regulation of copy number.
2. parA and parB for maintaining low copy number and avoiding two F plasmids in a single
cell during cell division.
3. A selectable marker for antibiotic resistance; some BACs also have lacZ at the
cloning site for blue/white selection.
4. T7 and Sp6 phage promoters for transcription of inserted genes.

48. • The first BAC vector,
 pBAC108L, did not contain a selectable marker for recombinants
• Two widely used BAC vectors,
 pBeloBAC11 and pECBAC1, are derivatives of pBAC108L
 The original cloning site is replaced with a lacZ gene carrying a multiple cloning site
 BACs are basically used in sequencing the genome of organisms in genome projects
(example: BACs were used in human genome project).
 Several hundred thousand base pair DNA fragments can be cloned using BACs

49. Figure: transforming a bacteriumusing a BACvector

50.  YACs are yeast expression vectors.
 First described in 1983 by Murray and Szostak
 As YAC vectors can accommodate 100-500 kb of insert DNA, the number of clones in a
genomic library can be greatly reduced.
 Mostly YACs are used for cloning very large DNA fragments and for the physical mapping of
complex genomes.
2. Yeast Artificial Chromosomes: YAC

51.  YAC vectors have following elements:
 E. coli origin of replication
 Yeast origin of replication
 Elements of eukaryotic yeast chromosome
(centromere and telomere region)
 Selection markers for both the host.

52.  Have advantageous over bacterial
artificial chromosomes (BACs)
 express eukaryotic proteins that
require post-translational
modification
 But, YACs are known to produce
chimeric effects which make them
less stable compared to BACs.

53.  Human artificial chromosomes (HACs) or mammalian artificial chromosomes (MACs) are
still under development.
 HACs are micro-chromosomes that can act as a new chromosome in a population of
human cells.
 HACs range in size from 6 to 10 Mb that carry new genes introduced by human
researchers.
 HACs can be used as vectors in transfer of new genes, studying their expression and
mammalian chromosomal function can also be elucidated using these micro-chromosomes
in mammalian system.
3. Mammalian Artificial Chromosomes: MAC

54.  Like YACs, rely on the presence of centromeric and telomeric sequences and origin of DNA
replication.
 They involve autonomous replication and segregation in mammalian cells
Two principal procedures exist for the generation of MACs
1. In one method, telomere-directed fragmentation of natural chromosomes is used. For
example, a human artificial chromosome (HAC) has been derived from chromosome 21
using this method.

55.  MAC vectors are difficult to assemble as compared to YAC vectors.
 Mammalian DNA has higher degree of repetition and larger centromere and telomere
regions
 MAC vectors have application in the field of gene therapy and eukaryotic protein
expression and production
2. Another method involves de novo assembly of cloned centromeric, telomeric, and
replication origins in vitro

56.  A vector used for expression of a cloned DNA
fragment in a host cell
 They are frequently engineered to contain regulatory
sequences that act as:
 promoter and/or enhancer regions and lead to
efficient transcription of the insert gene.
 Commonly used expression vector series are: pET
vectors, pBAD vectors etc
Expression Vector

57. Expression Vector
Designed specifically for the
expression of the transgene

58. For an expression vector following features are essential
 Promoter for initiation of transcription of gene of interest
 Terminator where transcription of gene ends
 Ribosome binding site
Examples of Expression Vector pET vector
 It is a cloning and expression vector system for recombinant protein production in E.coli
 Target genes are cloned under strong T7 bacteriophage promoter.
 The expression of the target protein is inducible by providing T7 RNA polymerase.

59. 1st target gene is initially cloned to non-
expression host cell. then transferred to a
expression host having T7 RNA Polymerase
gene in the genome.
Ampicillin and kanamycin resistance genes
are available in pET vectors as selection
marker.
pET28 and pET32 are the most commonly
used pET vectors

60.  used to aid molecular and genetics study of a
gene or protein
1. Promoter Probe Vectors
 Used for identification of efficient promoter
region in a DNA segment
 Promoter-less reporter genes (lacZ, GFP etc)
are used for construction of promoter probe
vectors
SpecializedExpression Vectors

61.  Some of the widely used promoter
probe vectors families are:
 pOT (eg. pRU1161, pRU1097 etc)
and
 pJP2 (eg. pRU1156, pRU1157 etc).
 pOT vectors have higher copy number
but lower stability as compared to
pJP2 vectors.

62. 2. Gene Fusion Vectors
 Used to produce fusion proteins
 Done by cloning two or more target genes with a reporter gene (His-tag, gfp, rfp, lacZ etc)
through the use of gene fusion vectors.
Viral Vectors
 Highly efficient in transferring target DNA/RNA segment
 Wildtype virus are modified by deleting the non-essential genes and incorporating
exogenous nucleic acid segments to construct a viral vector.
 Have wide application in gene therapy and targeted drug delivery systems.
 Main advantages are-high transfer efficiency and high cell specificity.

63. Commonly used viral vectors are:

64.  First mammalian expression vector whose genome size is 5.2kb.
 It is a DNA virus which can infect human as well other mammalian cell lines
 Recombinant SV40 vectors (rSV40) display some unique features:
 a well-known virus w/c can be produced in high titers.
 They can infect both resting and dividing cells.
 Stable transgene expression can be achieved in a wide range of cell types.
 The major disadvantageof SV40 vector is the low packaging capacity with insert size of <5kb
Simian Virus 40 (SV40)

65. Baculoviral Vectors
A DNA virus with host range restricted to invertebrates, mostly insects.
The infection is initiated by replication and transcription of the DNA genome
inside the nucleus and the assembly of the nucleo-capsids.
The nucleo-capsids then bud off from the plasma membrane and initiate systemic
infection
Recombinant baculoviral vectors have been constructed containing mammalian
cell specific promoters which can be used to infect mammalian cells as well

66. Advantages of baculoviral vectors:
 Since insects cells are higher eukaryotes,
desired post-translational modification (PTM)
of complex protein can be achieved.
 They have higher packaging capacity of insert.
 Lower biosafety issue.
 High level of protein expression.

67. There are few drawbacks of baculoviral vectors
 Foreign protein expressionusing an insect system is more complex and time
consuming than a bacterial system.
 Sometime protein post-translational processing may be sub-optimal to compensate
the secretory pathway of the protein.

68. Has several advantages over E. coli system due to presence of eukaryoticPTMmachinery.
Expression of complex proteins with proper modification and folding can be achieved by
yeast eukaryotic system
Different types of yeast vector include
1. YIp (yeast integrative plasmid)
 can integrate to the host genome by homologous recombination.
 This generally yields a single copy of recombinant vector DNA integrated to the host
genome.
Yeast Vector System

69. 2. YEp (yeast episomal plasmid)
 Can be maintained in the yeast system as an autonomously replicating episomal plasmid.
 This vector contains a part of 2µ plasmid which is essential for autonomous replication of the
vector.
3. YRp (yeast replicating plasmid)
 Are used to obtain a high copynumber inside the host (upto 100 copy number).
4. YCp(yeast centromere plasmid)
 Possess a centromeric region in addition to ARS which facilitates the mitotic segregation of the
linear plasmid during replication.
 The copy number of this vector is essentially one per cell

70. Selection of the transformed cells is done using
 Selectable marker genes that confers resistance to antibiotics
 Selection media containing the antibiotic (ampicillin, tetracycline etc.)
Selection of host cells/ organismcontainingvector sequences

71. 1. Blue-white screening system
(Vectors like pUC19, pGEM)
 Non-recombinant plasmids gives
blue-colour colony on the culture
medium
 Recombinant plasmids gives no
blue colour (white)
Screening clones havingdesired DNA inserts

72.  Insertion of gene of interest in a restriction site with in ampicillin gene
2. Insertional inactivation of antibiotic gene