RNA from the Hungarian isolate of poa semilatent virus (PSLV) directed synthesis of 120K, 75K, 25K (coat protein) and 20K polypeptides. translation of PSLV RNA was blocked by the cap analogue, mGpp, thus suggesting that the virus RNA was capped. PSLV RNA could be aminoacylated with [C]tyrosine . The sequence of 1.5 kb from the 3′ end of the PSLV RNA γ component revealed two open reading frames (ORFs) separated by a uridinerich intergenic region. The putative product of the incomplete 5′-proximal ORF showed a close amino acid sequence similarity with the C-terminal segment of the γa protein (putative RNA replicase) encoded in the barley stripe mosaic virus (BSMV) RNA γ, and the 20K product of the 3′-proximal ORF was found to be related to the 17K γb product of BSMV. The sequence of 0.8 kb from the 3′ end of PSLV RNA β encompassed two (incomplete) overlapping ORFs whose putative products are related to the βc and βd proteins encoded in the similarly arranged ORFs of BSMV RNA β. Nucleotide sequence homology between the respective parts of the two hordeivirus genomes was restricted to the ORF for γa, the spacer between the ORFs for γa and γb, and the 3′ non-coding region, particularly the 95 nucleotide segment at the 3′ end representing a tRNA-like structure. Despite limited sequence conservation beyond this segment, the entire 3′ non-coding region of PSLV RNA could be folded in a tight pseudoknotted structure closely resembling that of BSMV RNA. Surprisingly, the ‘signature’ sequence typical for BSMV RNA, internal polydisperse poly(A) intercalated between the coding part and the 3′ tRNA-like structure, was not detected in the PSLV genome. Instead, the virus RNA contained several oligoadenylate stretches spaced by other residues, close to the junction of its coding and 3′ non-coding portions.


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