Messenger RNA structure participating in the initiation of synthesis of cucumber mosaic virus coat protein

A single-stranded loop in the 5' untranslated region of cucumber mosaic virus RNA 4 contributes to competitive translational activity

The 5' untranslated region (UTR) of cucumber mosaic virus (CMV) RNA 4 confers a highly competitive translational advantage on a heterologous luciferase open reading frame. Here we investigated whether secondary structure in the 5' UTR contributes to this translational advantage. Stabilization of the 5' UTR RNA secondary structure inhibited competitive translational activity. Alteration of a potential single-stranded loop to a stem by substitution mutations greatly inhibited the competitive translational activity. Tobacco plants infected with wild type virus showed a 2.5-fold higher accumulation of maximal coat protein than did plants infected with a loop-mutant virus. Amplification of viral RNA in these plants could not explain the difference in accumulation of coat protein. Phylogenetic comparison showed that potential single-stranded loops of 12-23 nucleotides in length exist widely in subgroups of CMV.

The 5' untranslated region of cucumber mosaic virus RNA4 confers highly competitive activity on heterologous luciferase mRNA in cell-free translation

The cell-free translation of virion RNAs of several tripartite RNA viruses has shown that RNA4, a subgenomic RNA, is more competitive than other virion RNAs. Recently, the 3' untranslated region (UTR) of alfalfa mosaic virus (AMV) RNA4 was identified to be a competitive determinant. In this study, we observed that the RNA4 of cucumber mosaic virus (CMV), another tripartite RNA virus, was also found to be a strong competitor in translational competition among CMV virion RNAs. To identify the competitive determinant of CMV RNA4, we constructed various chimeric luciferase mRNAs containing RNA4 and/or vector-derived UTRs. The relative translations of luciferase-containing mRNA in the presence of a competitor mRNA showed that the 5' UTR, not the 3' UTR, substantially contributed to the highly competitive activity of CMV RNA4.

Nucleotide sequence analysis of cDNA encoding the coat protein of cucumber mosaic virus: genome organization and molecular features of the protein

The cDNA sequence coding for the coat protein of cucumber mosaic virus (Japanese Y strain) was cloned, and its nucleotide sequence was determined. The sequence contains an open reading frame that encodes the coat protein composed of 218 amino acids. The nucleotide and deduced amino acid sequences of the coat protein of this strain were compared with those of the Q strain; the homologies of the sequences were 78% and 81%, respectively. Further study of the sequences gave an insight into the genome organization and the molecular features of the coat protein. The coding region can be divided into three characteristic regions. The N-terminal region has conserved features in the positively charged structure, the hydropathy pattern and the predicted secondary structure, although the amino acid sequence is varied mainly due to frameshift mutations. It is noteworthy that the positions of arginine residues in this region are highly conserved. Both the nucleotide and amino acid sequences of the central region are well conserved. The amino acid sequence of the C-terminal region is not conserved, because of frameshift mutations, however, the total number of amino acids is conserved. The nucleotide sequence of the 3'-noncoding region is divergent, but it could form a tRNA-like structure similar to those reported for other viruses. Detailed investigation suggests that the Y and Q strains are evolutionarily distant.

Complete nucleotide sequence of two new satellite RNAs associated with cucumber mosaic virus

Complete nucleotide sequences of two new satellite RNAs (satRNA) of cucumber mosaic virus (CMV), E-satRNA and OY2-satRNA, have been determined and compared with known satellite RNA sequences. E-satRNA contained 339 nucleotide residues and OY2-satRNA had 386 nucleotide residues. Comparison of the sequences among satRNAs including these new satRNAs revealed extensive homologous regions in the 5'-terminus and the 3'-half. The former region contains about 95 nucleotide residues (80-100% homology) and the latter has about 175 nucleotide residues (81-99% homology), but there was less homology in the middle of the RNA. A possible secondary structure for E-satRNA, OY2-satRNA, and Y-satRNA [S. Hidaka et al. (1984) FEBS Lett. 174, 38-42] was constructed and compared with that of a satellite RNA from CMV-Q (Q-satRNA) [K. H. J. Gordon and R. H. Symons (1983), Nucl. Acids Res. 11, 947-960]. Two similar hairpin-loop structures in the 5'-terminal region were common features of the RNAs; one of them was found in E-satRNA, the other in OY2-satRNA, and both in Y-satRNA and Q-satRNA. Analyses of in vitro messenger properties of the satRNAs suggested that the first open reading frame of E-sat and Y-satRNAs was a possible coding region for protein synthesis.