COMPARISONS OF THE GENOMIC CIS-ELEMENTS AND CODING REGIONS IN RNA-BETA COMPONENTS OF THE HORDEIVIRUSES BARLEY STRIPE MOSAIC-VIRUS, LYCHNIS RINGSPOT VIRUS, AND POA SEMILATENT VIRUS

Nucleotide sequences of the genomic RNA beta components of hordeivirus es poa semilatent virus (PSLV) and lychnis ringspot virus (LRSV) were determined. PSLV and LRSV closely resemble barley stripe mosaic virus (BSMV), type hordeivirus, in the gene arrangement of their RNAs beta, comprising 5'-proximal beta a (coat protein) gene and downstream tripl e gene block (TGB) coding for the beta b, beta c, and beta d putative transport proteins. The beta a, beta b, beta c, and beta d proteins of the three hordeiviruses showed significant sequence similarity, with the respective proteins of PSLV and BSMV being closer to each other th an to their counterparts of LSRV. Comparisons of the TGB-encoded prote ins of hordeiviruses, potexviruses, carlaviruses, and furoviruses indi cate that the first and second TGB genes belong to the monophyletic gr oups, whereas the third gene may have multiple ancestry. LRSV, PSLV, a nd BSMV showed remarkable variation in the 3'-untranslated regions of their genomic RNAs. Among the three hordeiviruses, LRSV has the shorte st 3'-noncoding region that lacks tentative pseudoknot-forming element s conserved upstream of the 3'-tRNA-like structure in the BSMV and PSL V genomes. On the other hand, LRSV RNA beta, like that of BSMV, contai ned the internal poly(A) sequence that is absent from PSLV RNA. (C) 19 96 Academic Press, Inc.