PLANT CYTOSOLIC TRNA(HIS) POSSESSES AN EXCEPTIONAL C-54 IN THE CANONICAL T-PSI-C LOOP

A nuclear gene coding for tRNA(His) from Arabidopsis has been reported to contain C-54 in the T Psi C loop, although the corresponding nucle otide is an invariant U or a derivative in nearly all of her tRNAs. Th e only previously reported plant cytosolic tRNA(His) sequence, from lu pin, has U-54. To re-examine plant cytosolic tRNAs(His) and their gene s we have used DNA and RNA sequence analyses, restriction enzyme diges tion of PCR-amplified tRNA genes, RNA hybridization and in vivo aminoa cylation assails. Our results suggest that Arabidopsis nuclear tRNA(Hi s) genes ubiquitously contain C-54, as do those from tobacco, lupin an d pea. The C-54 nucleotide is maintained in the mature tRNA(His), whic h is aminoacylated in vivo, but to a relatively low level compared wit h other tRNAs examined. Finally it was shown that an Arabidopsis tRNA( His) gene with T-54 in place of C-54 is over 5-fold more transcription ally active than the wild-type gene using an in vitro system derived f rom plant nuclei. A possible role for this apparently sub-optimal tRNA (His) sequence is suggested.