OVERLAPPING GENES IN RNA PHAGE - NEW PROTEIN IMPLICATED IN LYSIS

We have identified a new 75 amino acid polypeptide (L protein) following f2 phage infection of E. coli. It is encoded by an out-of-phase overlapping gene which begins within the coat protein gene, ends in the replicase gene and covers the 36 base intercistronic space between them. A mutant f2 phage carrying a UGA mutation (op3), which complements mutations in the other three f2 genes (coat, A protein and replicase), fails to lyse cells (Model, Webster and Zinder, 1979) and also fails to produce L protein. Both lysis and L protein are restored following op3 infection of a UGA suppressor-containing strain or infection of wild-type bacteria with a revertant of op3. L protein is found in the insoluble fraction of artificially lysed cells. In this paper, we present the time course of its synthesis relative to the other f2-coded polypeptides: L protein synthesis increases as replicase synthesis decreases. We also report the discovery of another phage-coded polypeptide, which appears to be the product of a novel mode of translation: initiation at the coat protein initiation site, followed by translational frame shifting into the L protein frame and termination at the L protein terminus. © 1979.