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upon entry to the cell, phage head and tail proteins synthesised rapidly and new

functional phage assembled. The phage are subsequently released from the cell by

lysing the cell membrane to infect furtherE. colicells nearby. At the extreme ends

of the phagelare 12 bp sequences termedcos (cohesive) sites. Although they are

E.coli cell

Bacterial DNA

Bacteriophageλ

Injection of phage DNA

LYTIC PATH LYSOGENIC PATH

Phage DNA

Integration of

phage DNA

Bacterial DNA digested

New phage synthesised

Early protein synthesis Prophage

INDUCTION

Late protein synthesis

Host cell lysis

Cell division and

replication of bacterial

and phage DNA

Fig. 6.15The lysogenic and lytic cycles of bacteriophagel.

212 Recombinant DNA and genetic analysis