TRANSFER-RNA MIMICRY AMONG TYMOVIRAL GENOMIC RNAS RANGES FROM HIGHLY EFFICIENT TO VESTIGIAL

Three tRNA-associated properties of a representative set of tymoviral RNAs have been quantitatively assessed using higher plant (wheat germ) proteins: aminoacylation, EF-1 alpha . GTP binding, and 3'-adenylatio n of 3'-CC forms of the RNAs by CTP, ATP:tRNA nucleotidyltransferase. The RNAs fall into three classes differing in the extent of tRNA mimic ry. Turnip yellow mosaic (TYMV) and kennedya yellow mosaic virus RNAs had activities in all three properties similar to those of a higher pl ant tRNA(Val) transcript, and thus are remarkable tRNA mimics. Althoug h the isolated similar to 83 nt long tRNA-like structures showed high activity in these assays, in the case of TYMV, the 6318 nt long TYMV R NA was an even better substrate for valylation, Eggplant mosaic virus RNA, which has a differently constructed acceptor stem pseudoknot, dif fered from the above tymoviral RNAs in binding more weakly to EF-l alp ha . GTP. Erysimum latent virus RNA, which lacks an identifiable antic odon domain, could not be valylated and had very low 3'-adenylation ac tivity. The range of tRNA mimicry within the tymovirus genus thus rang es from extremely highly developed to minimal, The implications on the role of the tRNA mimicry in viral biology are discussed.