Elsevier

Virology

Volume 85, Issue 2, April 1978, Pages 475-486
Virology

Synthesis and processing of avian sarcoma virus glycoproteins

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Abstract

The avian sarcoma virus glycoproteins, gp85 and gp37, are formed by proteolytic cleavage of a glycosylated precursor polypeptide of molecular weight 95,000, pr95. In this communication we report on the intracellular site of synthesis and cleavage of this precursor polypeptide. Following a 30-min pulse label pr95 is found exclusively in the membrane fraction of infected cells in contrast to the other two precursor polypeptides, the gag precursor being located in both the membrane and cytoplasmic fractions and the gag-pol precursor located exclusively in the cytoplasmic fraction. Subfractionation of the membrane fraction revealed that pr95 was associated with the rough endoplasmic reticulum indicating that it was synthesized on membrane-bound polysomes. Pulse-chase experiments demonstrated that pr95 was cleaved within the membrane fraction and further fractionation indicated that this cleavage took place within the endoplasmic reticulum of the cell. The cleavage products gp85 and gp37 were then transported to the plasma membrane of the cell for incorporation into budding virus. These observations are discussed in relation to virus assembly.

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Supported by U.S. Public Health Services Research Grant CA 13213, Cancer Research Emphasis Grant CA 19725, and a Dernham Junior Fellowship awarded by the American Cancer Society, California Division.

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Present address: Imperial Cancer Research Fund, P. O. Box 123, Lincoln's Inn Fields, London WC2A 3PX, England.

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