Elsevier

Virology

Volume 38, Issue 4, August 1969, Pages 685-693
Virology

Conversion of the electrophoretic forms of cowpea mosaic virus in vivo and in vitro

https://doi.org/10.1016/0042-6822(69)90187-1Get rights and content

Abstract

The electrophoretic forms of purified cowpea mosaic virus (CPMV) and bean pod mottle virus (BPMV) were examined by disc electrophoresis. The slow-migrating form (S) of CPMV predominated in early infection, and the fast-migrating form (F) predominated in late infection. The reverse relationship was true for BPMV. The transition from S to F in CPMV and F to S in BPMV suggested a precursor-product relationship between the electrophoretic forms. Evidence for this relationship was provided by kinetic studies of 32P incorporation into the forms of CPMV and by short-interval sequential yield data. When separated by density gradient electrophoresis, the F form of both viruses demonstrated a greater specific infectivity than the S form. The S to F conversion of CPMV was simulated in vitro by reaction with a mixture of carboxypeptidases A and B or chymotrypsin. This conversion of the electrophoretic forms of CPMV resulted in an increase in specific infectivity. The F to S conversion of BPMV was observed only after exposure to trypsin.

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    Hence, here we report the crystal structure of eVLPs at 2.3 Å resolution and compare it with the cryo-EM structure of eVLPs (Hesketh et al., 2015) and the crystal structure of CPMV virion (PDB: 1NY7) (Lin et al., 1999; Stauffacher et al., 1987). In addition, we have carried out mass spectrometry-based proteomics analysis on the S subunits from CPMV eVLPs and virions to investigate in detail the location of the proteolytic cleavage sites of the S subunit that result in the occurrence of the slow and fast electrophoretic forms of the virus (Niblett and Semancik, 1969). Each protomer of CPMV that contains 587 amino acid (aa) residues undergoes proteolytic processing at residues Gln374-Gly375 by the viral protease prior or during assembly generating the large (L) and small (S) subunits (Franssen et al., 1982).

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Supported in part by U. S. Public Health Service Grant No. AI-06626.

2

The receipt of Public Health Service Predoctoral Fellowship (I-FI-GM-38, 984-01) is gratefully acknowledged. Present address Department of Plant Pathology, Kansas State University, Manhattan, Kansas 66502.

3

Present address: Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska 68508.

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