Sequence relationships among soil-borne wheat mosaic virus RNA species and terminal structures of RNA II

Gel-separated RNAs of the wild-type (WT), Lab 1 and Lab 2 isolates of soil-borne wheat mosaic virus (SBWMV) were transferred to nitrocellulose filters and hybridized with specific cDNA. RNA I, but not RNA II, from all three SBWMV isolates hybridized to cDNA copied from SBWMV WT RNA I. RNA II from all three SBWMV isolates hybridized to cDNA copied from SBWMV WT RNA II, confirming the hypothesis that the Lab 1 and Lab 2 isolates arose by deletion of part of RNA II of WT virions. RNA I1 from SBWMV WT (0-5L RNA) or from SBWMV Lab 1 (0.35L RNA) did not bind to oligo(dT)-ceUulose in high-salt buffer, or stimulate cDNA synthesis when primed with oligo(dT), suggesting that it has no 3'-poly(A) or oligo(A) sequences. No genome-linked protein was detected at the 5 ' ends of either RNA II by iodination, nor did the cap analogue 7-methylguanosine phosphate have an effect on their translation i vitro, indicating no cap structure at their 5 ' ends. RNA II was 5 ' end-labelled with [3-'P]ATP and T4 polynucleotide kinase after dephosphorylation with bacterial alkaline phosphatase, but all four bases were labelled, indicating heterogen-eity at the 5 " end. Soil-borne wheat mosaic virus (SBWMV) has a bipartite RNA genome separately encapsidated in rod-shaped virions (Shirako & Brakke, 1984a). Field plants usually have virion