title: The functional boundaries of the Q-utilization site required for antitermination of late transcription in bacteriophage lambda.
abstract: Expression of the late genes of bacteriophage lambda requires, in addition to the host functions, the lambda p'R promoter, the antiterminator sequence qut, and the product of gene Q which interacts with the Q utilization (qut) site. In the absence of the Q function or qut site, the p'R-initiated transcription is blocked by the t'R terminator at the 194th nucleotide downstream of the start point, s'R, producing a short 6 S mRNA. In this study the position and boundaries of the qut site were deduced by constructing plasmids containing various portions of the p'R-qut region, the t'R1 terminator, and the reporter gene galK. We measured galK gene expression in response to the gamma Q gene product supplied in trans by a prophage or Q-expression plasmid. We show that among the lambda proteins, the Q gene product alone is necessary and sufficient for complete qut-mediated transcription antitermination in vivo. These antitermination experiments, employing plasmids that contain different lengths of lambda p'R-qut sequence, identified the right boundary of the qut site, which is located between +4 and +18 (for s'R = +1). The functional left boundary of qut does not extend upstream from the -26th nucleotide of the p'R promoter, as based on the following experiments. The promoter function of the truncated (-26)p'R-s'R-(+18) sequence can be restored by fusion to the complete but qut-less p'R, pp, or PLac promoter; however, no antitermination was observed for such a p-(-26)p'R-s'R-(+18)-t'R-galK plasmid. Thus we conclude that the qut site partially overlaps with the p'R promoter sequence. However, promoters that contain the -10 region of p'R, s'R, and the +1 to +18 qut sequence did mediate Q-dependent antitermination when properly fused to the homologous or heterologous -35 promoter regions. Only those transcripts that start at s'R (+1 or very near to it) and also contain at least the first 18 nucleotides (actually greater than 4 and less than or equal to 18) of 6 S RNA appear to be a target for the Q-qut-mediated transcription antitermination, which acts not only at t'R but also at other Rho-independent or Rho-dependent terminators.
mesh_terms: D010582:Bacteriophage lambda / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D005786:Gene Expression Regulation; D005814:Genes, Viral; D011993:Recombinant Fusion Proteins / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: C027812:O protein, Bacteriophage lambda; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D014764:Viral Proteins