VIRION SWELLING IS NOT REQUIRED FOR COTRANSLATIONAL DISASSEMBLY OF COWPEA CHLOROTIC MOTTLE VIRUS IN-VITRO

The mechanism by which virions of cowpea chlorotic mottle virus (CCMV) disassemble and allow for translation of the virion RNA is not well u nderstood, Previous models have suggested that virion swelling is requ ired to expose the virion RNA for translation in a process referred to as cotranslational disassembly (M. Brisco, R. Hull, and T. M. A. Wils on, Virology 148:210-217, 1986; J. W. Roenhorst, J. W. M. van Lent, an d B. J. M. Verduin, Virology 164:91-98, 1988; J. W. Roenhorst, J. M. V erduin, and R. W. Goldbach, Virology 168:138-146, 1989), Previous work in our laboratory has identified point mutations in the CCMV coat pro tein which result in virions with altered swelling characteristics (J. Fox, F. G. Albert, J. Speir, and M. J. Young, Virology 227:229-233, 1 997; J. M. Fox, X. Zhao, J. A. Speir, and M. J. Young, Virology 222:11 5-122, 1996), The mild-type and mutant CCMV virions were used to corre late virion swelling with the ability of virion RNA to be translated i n a cell-free wheat germ extract, Mutant virions unable to swell (cpK4 2R) are as infectious as wild-type virions in vivo, and the levels of translated encapsidated virion RNA are similar to those of wild-type v irions in vitro, Mutant virions capable of swelling but not of disasse mbling in vitro (cpR26C) are noninfectious and have severely reduced l evels of translation of the encapsidated virion RNA in vitro. These st udies suggest that virion swelling is not required for the cotranslati onal disassembly of CCMV. Additionally, the results indicate that ther e is a pH-dependent structural transition in the virion, other than sw elling, that results in the RNA's being exposed for translation in vit ro, An alternative model suggesting that cotranslational disassembly o f CCMV involves presentation of the virion RNA through the virion five fold axis is proposed.