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lZapis a commercially produced cloning vector that includes unique cloning sites

clustered into a multiple cloning site (MCS) (Fig. 6.18). Furthermore the MCS is located

within alacZregion providing a blue/white screening system based on insertional

inactivation. It is also possible to express foreign cloned DNA from this vector. This is

a very useful feature of somelvectors since it is then possible to screen for protein

Insertion Vectors (λgt10) Replacement Vectors (λEMBL4)

EcoRI EcoRI BamHI

CI857 CI857

Digest with restriction enzyme Digest with two restriction enzymes

Insert DNA fragment Remove stuffer fragment

Insert DNA fragment

Fig. 6.17General schemes used for cloning inlinsertion andlreplacement vectors.Cl857 is a temperature-

sensitive mutation that promotes lysis at 42C after incubation at 37C.

SacINotIXbaISpeI EcoRIXhoI

COS

Cos

Cos

T3

promoter

T7

promoter

DNA synthesis

host lysis genes

CI857

Multiple cloning site in lacZ gene

Capsid

components

Lytic control COS

T I

A–J

Bluescript

phagemid

site

Fig. 6.18General map oflZap cloning vector, indicating important areas of the vector. The multiple cloning

site is based on thelacZgene, providing blue/white selection based on theb-galactosidase gene. In between

the initiator (I) site and terminator (T) site lie sequences encoding the phagemid Bluescript.

214 Recombinant DNA and genetic analysis