Structure and Function of an Intercistronic Regulatory Region in Bacteriophage Lambda

Abstract

INTRODUCTION
When bacteriophage λ infects Escherichia coli, two possible pathways of development may ensue. The virus may undergo a lytic mode of growth resulting in the formation and release of progeny virus concomitant with lysis of the host cell. Alternatively, the phage may enter a lysogenic state in which the viral DNA integrates into the bacterial genome and concurrently represses expression of viral functions. Crucial to the establishment of lysogeny is the synthesis of two phage functions: the integration protein, which catalyzes the genetic recombination between the viral DNA and the host genome, and the repressor protein, which directly inhibits transcription of phage functions. In simple terms, the viral infection can be considered a competition between the accumulation of those gene products which commit the virus to lytic development and the expression of gene products which turn on synthesis of the phage repressor protein, thereby committing the infection to lysogeny. Under normal growth conditions, a delicate balance is achieved whereby both lytic and lysogenic patterns of development are expressed in a single viral infection (for review, see Weisberg et al. 1977).

Immediately after λ infection, transcription is initiated by the host RNA polymerase from two major promoters, P_R and P_L, located within the phage immunity region (see Fig. 1). At early times the majority of this transcription, both rightward and leftward, is limited to the immunity region by sites of transcription termination, t_RI and t_L, respectively (Fig. 1). Efficient transcription distal to these two termination sites depends upon expression of...