The molecular basis for the differential translation of TMV RNA in tobacco protoplasts and wheat germ extracts

Abstract

Translation of tobacco mosaic virus (TMV) RNA in tobacco protoplasts yields the 17.5‐K coat protein, a 126‐K protein and a 183‐K protein which is generated by an efficient readthrough over the UAG termination codon at the end of the 126‐K cistron. In wheat germ extracts, however, only the 5′‐proximal 126‐K cistron is translated whereas the 183‐K readthrough protein is not synthesized. Purification and sequence analysis of the endogenous tyrosine tRNAs revealed that the uninfected tobacco plant contains two tRNAsTyr, both with GΨA anticodons which stimulate the UAG readthrough in vitro and presumably in vivo. In contrast, ˜85% of the tRNATyr from wheat germ contains a QΨA anticodon and ˜15% has a GΨA anticodon. Otherwise the sequences of tRNAsTyr from wheat germ and tobacco are identical. UAG readthrough and hence synthesis of the 183‐K protein is only stimulated by tRNATyrGΨA and not at all by tRNATyrQΨA. The tRNAsTyr from wheat leaves were also sequenced. This revealed that adult wheat contains tRNATyrGΨA only. This is very much in contrast to the situation in animals, where Q‐containing tRNAs are characteristic for adult tissues whereas Q deficiency is typical for the neoplastic and embryonic state.

Cell-free Translation of Beet Necrotic Yellow Vein Virus: Readthrough of the Coat Protein Cistron

“…The foregoing observations are consistent with a translation strategy for BNYVV RNA-2 involving partial readthrough of the termination codon of the viral coat protein cistron to produce P85, Beier et al (1984) have recently isolated and characterized two closely similar tRNA tyr species from tobacco which can further stimulate readthrough of the tobacco mosaic virus (TMV) 126K amber termination codon. We have found that the tobacco suppressor tRNA tyr has a similar effect on translation of BNYVV RNA-2.…”

Stop making sense or Regulation at the level of termination in eukaryotic protein synthesis

“…This observation suggests that the presence of the Q modification in the wobble position of the anticodon restricts recognition of the tRNA to the cognate UAC and UAU Tyr codons whereas the presence of an unmodified G permits the additional recognition of UAG. A correlation between suppression activity and undermodification in the wobble position was also observed in wheat germ [23] and lupin tRNAs [24].…”

“…It has been proposed [23] that the G of the anticodon could adopt a 'syn' conformation that would allow it to hydrogen bond with the G of the codon. On the contrary, the presence of a bulky side chain which projects out of the Q!PA anticodon loop [25], would prevent by steric hindrance the Q nucleoside from adopting such a conformation.…”

The tRNATyr multigene family of Triticum aestivum: genome organization, sequence analyses and maturation of intron‐containing pre‐tRNAs in wheat germ extract

“…The 0.5 kb EcoRI fragment of pTtY5 was completely sequenced. A comparison with the two major cytoplasmic tRNA Ty~ isoacceptors from wheat [26] reveals that four of the nine sequenced Triticum tRNA Ty~ genes code for tRNA~ yr, whereas two code for tRNAff y~ (Fig. 2).…”