SITE-DIRECTED MUTAGENESIS OF A POTYVIRUS COAT PROTEIN AND ITS ASSEMBLY IN ESCHERICHIA-COLI

Multiple copies of the Johnsongrass mosaic virus coat protein synthesi zed in Escherichia coli can readily assemble to form potyvirus-like pa rticles. This E. coli expression system has been used to identify some of the key amino acid residues, within the core region of the coat pr otein, required for assembly. The two charged residues R194 and D238 p reviously proposed theoretically to be involved as a pair in the const ruction of a salt bridge crucial for the assembly process were targete d for site-directed mutagenesis. The results from our experiments sugg est that the two residues are required for the assembly process but ar e not necessarily involved as a pair in a common salt bridge.