Uzan M: Sequence and characterization of the bacteriophage T4 comC alpha gene product, a possible transcription antitermination factor

We have sequenced a 1,340-bp region of the bacteriophage T4 DNA spanning the comCa gene, a gene which has been implicated in transcription antitermination. We show that comCav, identified unambiguously by sequencing several missense and nonsense mutations within the gene, codes for an acidic polypeptide of 141 residues, with a predicted molecular weight of 16,680. We have identified its product on one- and two-dimensional gel systems and found that it migrates abnormally as a protein with a molecular weight of 22,000. One of the missense mutations (comCa803) is a glycine-to-arginine change, and the resulting protein exhibits a substantially faster electrophoretic mobility. The ComCa protein appears immediately after infection. Its rate of synthesis is maximum around 2 to 3 min postinfection (at 37°C) and then starts to decrease slowly. Some residual biosynthesis is still detectable during the late period of phage development. The notion that termination and antitermination mecha-nisms may be operating in bacteriophage T4 development initially came from the observation of a strong polarity on early transcription when infection is carried out in the absence of translation. In vivo experiments that used inhib-itors of protein synthesis, as well as in vitro studies, have shown that this polarity is due to the action of the host transcription terminator p (2). The question of whether translation of phage RNA is required just to mask potential rho-dependent termination sites and/or to allow the synthe-sis of viral antitermination proteins could not be answered on the basis of experiments that used inhibitors of protein synthesis. Furthermore, analysis of this problem is compli-cated by the fact that many genes, transcribed by elongation of transcripts initiated at distal early promoters, are also transcribed from proximal promoters (the middle promoters