Translation of the RNA of Cowpea Severe Mosaic Virus in vitro and in Cowpea Protoplasts

Abstract

The multiplication of the DG strain of cowpea severe mosaic virus (CPsMV-DG) was studied in cowpea protoplasts prepared from infected leaves and in protoplasts inoculated in vitro. Up to 6 proteins were detected in DG-infected cells which were either absent in mock-infected protoplasts or present in smaller amounts. Their MW were estimated to be 125,000 [125 kilodalton (K)], 98 K, 86 K, 65 K, 39 K and 22 K. The latter 2 probably represent the 2 viral capsid proteins. The 125 K MW protein was found early in infection and was synthesized at a high rate throughout infection. It was detected, together with the 86 K MW protein, in protoplasts that had been inoculated with purified bottom component alone. CPsMV was translated in a messenger-dependent reticulocyte lysate. Total DG strain RNA directed the synthesis of polypeptides with MW of 200 K, 125 K, 108 K, 98 K and 42 K. No cleavage of the in vitro products was observed by varying the temperature or the concentration of dithiothreitol (DTT) in the translation mixture. The polypeptides induced by CPsMV-DG were compared with those induced by the SB strain of cowpea mosaic virus. Since the 170 K and 30 K MW proteins typical of the SB strain were not detected among the DG-specific proteins either in vivo or in vitro, a different processing of the large precursor of 200 K MW seems to take place.