M13
Phage
as
Vectors
for
DNA
Sequencing - M13 is a filamentous bacteriophage of E. coli and contains a 7.2 kb long single stranded circular DNA. M13 phage has been variously modified to give rise to a M13 mp series of cloning vectors which can be used for cloning of a wide variety of DNA fragments particularly for the purpose of sequencing through Sanger's method of dideoxy chain termination.
Cloning vectors of M13 mp series have a lac Z gene that complements gal host (e.g. JM 103 or JM 104) giving blue colonies.
But if a foreign DNA segment is inserted at one of the polylinker sites associated with lac Z gene, it inactivates lac Z gene and no complementation is possible.




