PRIMARY STRUCTURES OF BOTH SUBUNITS OF ESCHERICHIA-COLI GLYCYL-TRANSFER RNA-SYNTHETASE

Google Scholar
  • 1 January 1983
    • journal article
    • research article
    • Vol. 258  (17) , 637-641
Abstract
E. coli glycyl-tRNA synthetase is one of 2 aminoacyl-tRNA synthetases which is comprised of 2 different subunits (in an .alpha.2.beta.2 structure). The 2 coding regions occur in tandem in the order .alpha. + .beta. and are synthesized from a single mRNA. Primary structures of both proteins were determined by DNA sequencing of each coding region and by analysis of tryptic fragments of the enzyme. The .alpha.-subunit is 303 codons and terminates with TAA; the .beta.-subunit is 689 codons followed by tandem TAA stops. S1 nuclease mapping of the 3''-end of the 2-cistron glyS mRNA showed that it predominantly ends 33/34 bases beyond the tandem stops with an RNA polymerase terminator sequence. Altogether, 43% of the translated polypeptide sequences were confirmed by mass spectrometric analysis of peptide fragments including confirmation of the COOH-terminal end of the .beta.-china. This involved determinations, by fast atom bombardment mass spectrometry, of the masses of numerous whole tryptic fragments and of fragments truncated by 1-3 cycles of Edman degradations. The primary structures of the 2 subunits show no homologies with each other and have no internal sequence repeats of significance. While there are no extensive homologies with 5 other sequenced, or partially sequenced, synthetases, the .alpha.-subunit has a short sequence which can be aligned with sequences found in functionally important areas of 2 other synthetases and in uncharacterized parts of a third and fourth synthetase.