w 392 Chapter 17 The Viruses:Bacteriophage NA is doubl stranded.nd 6 (o ePrescott−Harley−Klein: Microbiology, Fifth Edition VI. The Viruses 17. The Viruses: Bacteriophages © The McGraw−Hill Companies, 2002 392 Chapter 17 The Viruses: Bacteriophages Leftward Transcription Lysis S R A W B C D E F Z U V G H M L K I J b2 att int xis gam red PL PR P O DNA synthesis Repression Early control Repression Recombination Excision and integration Tail synthesis Head synthesis Late control Maturation Rightward Transcription clll N cl cro cll Q Figure 17.16 The Lambda Phage Genome. The direction of transcription and location of leftward and rightward promoters (PL and PR) are indicated on the inside of the map. The positions of major regulatory sites are shown by lines on the map and regulatory genes are in blue. Lambda DNA is double stranded, and transcription proceeds in opposite directions on opposite strands. 17 bp N 1 2 3 4 5 5 4 1 2 3 N Figure 17.17 Lambda Repressor Binding. (a) A computer model of lambda repressor binding to the lambda operator. The lambda repressor dimer (brown and tan) is bound to DNA (blue and light blue). The arms of the dimer wrap around the major grooves of the double helix. (b) A diagram of the lambda repressor-DNA complex. The repressor binds to a 17 bp stretch of the operator. The 3-helices make closest contact with the major grooves of the operator (the helices are labeled in order, beginning at the N terminal of the chain). (a) (b)