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 comC alpha gene, a gene which has been implicated in transcription antitermination. We show that comC alpha, 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 (comC alpha 803) is a glycine-to-arginine change, and the resulting protein exhibits a substantially faster electrophoretic mobility. The ComC alpha protein appears immediately after infection. Its rate of synthesis is maximum around 2 to 3 min postinfection (at 37 degrees C) and then starts to decrease slowly. Some residual biosynthesis is still detectable during the late period of phage development.