Virus-specific protein synthesis in cells infected by infectious pancreatic necrosis virus

Abstract

A study of virus-specific protein synthesis in infectious pancreatic necrosis virus-infected [rainbow trout gonad] RTG-2 cells was undertaken to find a relationship between the coding capacity of the virus genome (2 segments of double-stranded RNA of MW 2.5 .times. 106 and 2.3 .times. 106) and the sizes and relative amounts of polypeptides in the virion and in infected cells. The time course of virus-specific protein synthesis was followed by pulse labeling infected UV-irradiated cells with [35S]methionine and analyzing the labeled proteins by polyacrylamide gel electrophoresis followed by autoradiography. Three size classes of virus-specific polypeptides were synthesized, in the same relative proportion, throughout the infectious cycle, beginning 3 h postinfection. Their designation and MW were .alpha.1, 100,000; .alpha.2, 90,000; .beta.1, 59,000; .beta.2, 56,000; .gamma.1, 32,000; .gamma.2, 30,000; and .gamma.3, 28,000. Experiments using amino acid analogs, protease inhibitors, ZnCl2 and supraoptimal temperatures showed that polypeptides of the .beta. and .gamma. families did not arise from the .alpha. polypeptides by post-translational cleavage. Slow cleavage late in the infectious cycle could be demonstrated, since during a 12 h period radioactivity was chased from .beta.1 via .beta.3 to .beta.4 (MW 50,000) and .beta.5 (MW 49,000). During the chase most of .gamma.2 was degraded, but radioactivity could not be chased from the remaining virus-specific polypeptides. Purified virus contained polypeptides .alpha.1, .alpha.2, .beta.4, .beta.5 and .gamma.1. The .beta. polypeptides made up > 60% of the virion proteins. Infectious pancreatic necrosis virus probably possesses a unique mechanism for synthesis of 3 size-classes of proteins using mRNA transcripts from 2 high-molecular-weight double-stranded RNA genome segments.