A single amino acid mutation in the Carnation ringspot virus capsid protein allows virion formation but prevents systemic infection

A Carnation ringspot virus (CRSV) variant (1.26) was identified that accumu lates virions but is incapable of forming a systemic infection. The 1.26 ca psid protein gene possesses a Ser-Pro mutation at amino acid 282. Conversio n of 1.26 amino acid 282 to Ser restored systemic infection, while the reci procal mutation in wild-type CRSV abolished systemic infection. Similar mut ations introduced into the related Red clover necrotic mosaic virus capsid protein gene failed to induce the packaging but nonsystemic movement phenot ype. These results provide additional support for the theory that virion fo rmation is necessary but not sufficient for systemic movement with the dian thoviruses.