Swelling of isometric and of bacilliform plant virus nucleocapsids is required for virus-specific protein synthesis in vitro.

Encapsidated RNA of cowpea chlorotic mottle virus (CCMV), brome mosaic virus (BMV), alfalfa mosaic virus, and southern bean mosaic virus can act as templates for protein synthesis when preswollen virions are added to a wheat germ extract, or when unswollen virions swell in the extract. Encapsidated RNA of turnip yellow mosaic virus, whose particles are unlikely to swell under the conditions used here, did not act as a template. CCMV and BMV, swollen in the extract, gave relatively more RNA 1 and 2 products than when preswollen by dialysis.