Structure and mechanism in transcriptional antitermination by the bacteriophage lambda N protein.

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Each of the two early operons and the late operon ofbacteriophage λ contain transcriptional terminators (Fig.1a). As a consequence, the pattern of transcription duringa lytic infection by λ can be viewed as a cascade of transcriptional antitermination mechanisms (for review, seeDas 1993; Greenblatt et al. 1993; Friedman and Court1995; Richardson and Greenblatt 1996). These antitermination mechanisms are "processive" in the sense that theycan influence termination through multiple terminatorsover many kilobases of DNA and many minutes of transcription time. The N gene is the first gene to be transcribed in the leftward early pL operon and encodes an antitermination factor. Once N protein is made, it modifiesEscherichia coli RNA polymerase transcribing the earlypL and pR operons so that the RNA polymerase transcribes efficiently through all the intrinsic and Rho-dependent terminators of both operons. This leads to the e...