Molecular Interactions of tRNA (Transfer Ribonucleic Acid) Synthase I (PSUI)

摘要

The hisT operon of E. coli codes for at least two protein products. The downstream region codes for the modification enzyme, transfer ribonucleic acid (tRNA) psi synthase I (PSUI). The adjacent upstream gene specifies a 36.4kd polypeptide of unknown function. Although the expression of these two proteins is coupled, they appear to be functionally independent. Purified PSUI modified all the hisT isoacceptors of tRNA(His), tRNA(Tyr) and tRNA(Leu) to their wild-type counterparts. Since the tRNAs contain all known arrangements of psi at positions 38, 39 and 40, the 36.4-kd polypeptide cannot be a functional subunit of PSUI, or another synthase acting at one of these sites. Preliminary evidence indicates that PSUI also acts on an unprocessed precursor transcript and an anticondon stem-loop fragment to tRNA(Phe), both prepared in vitro.