Biotechnology Engineering

1. 1
Lecture- 6

2. Cosmids
Types of
cosmids:
Single cos
cosmids : pJB8
Dual cos cosmids :
c2XB, supercos -1,
pLFR - 5
Cosmid is a plasmid containing one or two copies of cos sites of
bacteriophage lambda. It is useful as a vector for gene cloning in
conjunction with a packaging system
The concatemers of cosmid molecules linked at their cos sites act as
substrate for in vitro packaging
The host containing cosmids do not form plaques but form colonies
Cosmids have high insert capacities i.e., 30 -45 kbp
2

3. Fig : Single cos
cosmids
Fig : Dual cos
cosmids
3

4. in vitro
packaging
system
Cloning strategies used with cosmid vectors
4

5. Another cloning strategy
for single cos site vector
5

6. Can be used as gene cloning vectors
Cosmids are high insert capacity vectors
Cosmids are used for the analysis of complex genomes
Large genes can be studied intact and genetic linkage
studies can be carried out at molecular level
Background molecules which do not have the insert DNA
or have the smaller inserts are eliminated during
packaging
Transformation frequency of cosmids is high
Advantages of cosmids
6

7. Phagemid vectors
Phagemid is a filamentous phage-derived vector
containing the replication origin of a plasmid
Properties
Small size
High genetic stability
Can be used to clone single and double stranded
DNA
7

8. Phagemid contains two origins of replication:
Plasmid s and phage's
Replicates like
plasmid producing
double-stranded
plasmid DNA which has
conventional properties
Replicates like M13
producing single
stranded DNA, packaged
and released in presence
of a helper phage
sequencing work can be done directly, without
sub-cloning from the plasmid to phage
This process is called
DNA rescue
8