Structure of the phenylalnyl-tRNA synthetase genes fromThermus thermophilusHB8 and their expression inEscherichia coli

Abstract

A 4459 bp long BamHI restriction fragment containing the two genes for the Thermus thermophilus HB8 phenylalanyt-tRNA synthetase was cloned in Escherichia coll and its nucleotlde sequence was determined. The genes pheS and pheT encode the α- and β-subunlts with a molecular weight of 39 and 87 kD, respectively. Three conserved sequence motifs typical for class II tRNA synthetases occur in the α-subunit. Secondary structurepredictions indicate that an arm composed of two antiparallel α-helices similar to that reported for the E.coll seryl-tRNA synthetase may be present in its N-terminal portion. In the β-subunlt clusters of hydrophillc amino acids and a leucine zipper motif were identified, and several pronounced α-hellcal regions were predicted. The particular arginine and lyslne residues in the N-terminal portion of the β-subunit, which were found to participate in tRNA binding in the yeast and E.coli PheRSs, have their counterparts in the T.thermophilus protein. The 5′-portion of an open reading frame downstream of pheT was found and codes for a yet unidentified, extremely hydrophobic peptkte. The pheST genes are presumably cotranscribed and translatlonally coupled. A novel type of a putative transcriptional terminator in Thermus species was identified immediately downstream of pheT and other Thermus genes. The genes pheS and pheST were expressed in E.coli.