Protein synthesis in fat body of Trichoplusia ni during the course of a nuclear polyhedrosis virus infection

Abstract

Protein synthesis in fat body of cabbage looper, Trichoplusia ni, larvae was investigated during the course of a nuclear polyhedrosis virus infection. Fat body total protein concentration increased late in the disease due to a large increase in the saline-insoluble protein fraction. Incorporation of 14C-leucine into fat body proteins in vitro revealed a slight increase in synthesis of both retained and released proteins on the first day of the disease followed by a rapid decrease in protein synthesis. The rate of decrease was more rapid in released than in retained proteins. Fat body soluble proteins of healthy larvae were separated into 22 bands by disc acrylamide gel electrophoresis. In diseased larvae, the concentration of major protein bands decreased during late stages of the disease. Electropherograms of the soluble fraction following 14C-leucine incorporation revealed most protein synthesized in the fifth instar of healthy larvae was in 2 zones close to the origin of the gels. These proteins were rapidly released following synthesis and accounted for all but trace amounts of the released protein. Synthesis of these major proteins decreased rapidly in diseased larvae after the first day as did synthesis of released proteins. Radioactivity in other areas of the gels was well maintained in retained proteins of diseased larvae until the fourth day when little radioactivity was present in any area of the gel.