M.SC. BOTANY SEM - III MGSU, BIKANER

Cosmids:- > It is first described by Collins and Hohn in 1978. > It is formed by joining ends of a linearized plasmid DNA with cos-site of lambda DNA. > It is the commonly used cloning vector suitable for cloning large DNA fragments upto 45 kbp. > Cosmid has an origin of replication, selectable markers, and gene cloning sites of plasmid DNA. Salient features:- i. Cosmid is a circular ds DNA. ii. It has two complementary single-stranded regions at both ends of a plasmid DNA. The two cos-ends form a duplex by base pairing. iii. The cosmid DNA does not code for phage proteins and host cell lysis. iv. It does not involve in multiplication of phage particles. v. It has an origin of replication from plasmid DNA for independent replication. vi. It has selectable marker genes and gene cloning sites of plasmid DNA vii. The cosmid DNA is packed within protein coat of bacteriophage to form inactive phage particles. Cos-site is a prerequsites for invitro packaging of cosmid in phag...