Poa semilatent virus, a hordeivirus having no internal polydisperse poly(A) in the 3' non-coding region of the RNA genome

Abstract

RNA from the Hungarian isolate of poa semilatent virus (PSLV) directed in vitro synthesis of 120K, 75K, 25K (coat protein) and 20K polypeptides. In vitro translation of PSLV RNA was blocked by the cap analogue, m7Gpp, thus suggesting that the virus RNA was capped. PSLV RNA could be aminoacylated with [~4C]tyrosine in vitro. The sequence of 1-5 kb from the 3' end of the PSLV RNA y 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 7a protein (putative RNA replicase) encoded in the barley stripe mosaic virus (BSMV) RNA 7, and the 20K product of the 3'-proximal ORF was found to be related to the 17K 7b product of BSMV. The sequence of 0-8 kb from the 3' end ofPSLV RNA fl encompassed two (incomplete) overlapping ORFs whose putative products are related to the tic and fld proteins encoded in the similarly arranged ORFs of BSMV RNA ft. Nucleotide sequence homology between the respective parts of the two hordeivirus genomes was restricted to the ORF for 7a, the spacer between the ORFs for ya and yb, and the 3' non-coding region, particularly the 95 nucleotide segment at the 3' end representing a tRNAlike 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.

The barley stripe mosaic virus gamma b gene encodes a multifunctional cysteine-rich protein that affects pathogenesis.

“…Another structurally interesting feature of the BSMV yb protein is the organization of cysteine and histidine residues into two clusters ( Figure 2) that resemble the metal binding "zinc finger" motifs characteristic of many eukaryotic transcription factors (Morozov et al, 1989;Struhl, 1989). These two yb cysteine-rich clusters are separated by the basic motif (Koonin et al, 1991), and they have significant homology with cysteinerich motifs found in an analogous protein (Agranovsky et al, 1992) of poa semilatent virus (PSLV), a related hordeivirus (Hunter et al, 1986).…”

“…To provide an analysis of the role of yb in barley .~ \ , (Agranovsky et al, 1992) are shown, and serine (S) and leucine (L) substitutions are indicated by unfilled capital letters. The basic motif (EM) immediately adjacent to cluster C1 corresponds to a conserved "tether" domain region of chloroplast intron-encoded proteins (CIPs; Koonin et al, 1991).…”

RNA-binding activities of barley stripe mosaic virus b fusion proteins

“…We have previously shown that amino acid substitutions within the cysteine-rich C1 and C2 clusters of 7b, and the basic motif separating the clusters, have profound effects on the disease phenotype in barley (Donald & Jackson, (Agranovsky et al, 1992) are shown, and serine (S) and leucine (L) substitutions are indicated by outlined capital letters. The basic motif (BM) immediately adjacent to cluster C1 corresponds to a conserved 'tether' domain region of CIPs (Koonin et al, 1991).…”

“…The two ~b clusters are separated by a basic region related in sequence to putative chloroplast tRNA intron-encoded proteins (CIPs) and positively charged residues similar to those of the 'tether' domains 0001-3714 © 1996 SGM of reverse transcriptases (Koonin et al, 1991). BSMV 7b also has considerable homology to an analogous protein encoded by poa semilatent virus (PSLV) (Agranovsky et al, 1992), a closely related hordeivirus (Hunter et al, 1986).…”

“…Cysteine residues were changed to serines, and the single histidine in cluster 2 was changed to a leucine. Additional mutations were introduced into the basic motif separating the two cysteine-rich clusters to modify amino acids that are conserved when compared to sequences of the related PSLV yb protein (Agranovsky et al, 1992), or the ' tether' domain of the chloroplast intron proteins (CIP) (Koonin et al, 1991). Mutation 26 substitutes glutamine and asparagine for the adjacent arginine and lysine residues that are located at the carboxy-terminal side of the last cysteine residue of cluster 1.…”