Sequences 5 ' of the conserved tRNA-like promoter modulate the initiation of minus-strand synthesis by the brome mosaic virus RNA-dependent RNA polymerase
Mr. Chapman et al., Sequences 5 ' of the conserved tRNA-like promoter modulate the initiation of minus-strand synthesis by the brome mosaic virus RNA-dependent RNA polymerase, VIROLOGY, 252(2), 1998, pp. 458-467
Each of the brome mosaic virus (BMV) genomic RNAs contains a conserved tRNA
-like structure that is sufficient to direct minus-strand RNA synthesis in
vitro. The tRNA-like promoters, tB1 and tB3, direct approximately equal amo
unts of synthesis in vitro. However, 5' sequences were found to affect the
amount of minus-strand synthesis, suggesting that sequences beyond the tRNA
-like structure are important in moderating minus-strand synthesis. Consist
ent with this, sequences upstream the tRNA-like structure are able to parti
ally suppress mutations at or near the initiation site. This activity is ob
served in the 5' sequences of both BMV and CMV (cucumber mosaic virus) temp
lates. However, a chimeric RNA containing the CMV tRNA-like promoter fused
to the 5' sequences of BMV was not able to suppress mutations at the initia
tion site, suggesting that homologous 5' and 3' sequences are required to a
ffect initiation. The ability to suppress mutations at the initiation site
was correlated with a slight increase in the ability of the BMV RNA-depende
nt RNA polymerase to interact with the RNA. (C) 1998 Academic Press.