THE CARBOXY-TERMINAL 2-3RDS OF THE COWPEA CHLOROTIC MOTTLE BROMOVIRUSCAPSID PROTEIN IS INCAPABLE OF VIRION FORMATION YET SUPPORTS SYSTEMICMOVEMENT

Previous investigations into recombination in co pea chlorotic mottle bromovirus (CCMV) resulted in the recovery of an unusual recombinant v irus, 3-57, which caused a symptomless infection of cowpeas but formed no detectable virions. Sequence analysis of cDNA clones derived from 3-57 determined that mutations near the 5' terminus of the capsid prot ein gene introduced an early translational termination codon. Further mutations introduced a new in-frame start codon that allowed translati on of the 3' two-thirds of the capsid protein gene. Based on the mutat ions observed in 3-57, wild-type CCMV clones were modified to determin e if the carboxyl two-thirds of the capsid protein functions independe ntly of the complete protein in long-distance movement. Analysis of th ese mutants determined that while virion formation is not required for systemic infection, the carboxy-terminal two thirds of the capsid pro tein is both required and sufficient for systemic movement of viral RN A. This indicates that the CCMV capsid protein is multifunctional, wit h a distinct long-distance movement function in addition to its role i n virion formation.