METHIONYL-TRANSFER RNA-SYNTHETASE FROM ESCHERICHIA-COLI - PRIMARY STRUCTURE OF THE ACTIVE CRYSTALLIZED TRYPTIC FRAGMENT

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 127  (3) , 449-457
Abstract
A 3300-base segment of E. coli chromosomal DNA, cloned into plasmid pBR322, will complement a methionine auxotroph in which the lesion is a defective methionyl-tRNA synthetase (EC 6.1.1.10) with a much reduced affinity for methionine. Crude extracts of these transformants contain elevated levels of a protein which has a subunit MW of 66,000, methionyl-tRNA synthetase aminoacylation activity in vitro and which cross-reacts with anti-(methionyl-tRNA synthetase) antibodies. This polypeptide is very slightly larger than the well-characterized and crystallized tryptic fragment of methionyl-tRNA synthetase. A DNA sequence of 1750 residues at 1 end of the cloned insert codes for a non-terminated open reading frame in which a large number of methionyl-tRNA synthetase tryptic and chymotryptic peptides can be located. The segment extending 300 nucleotides upstream of this coding segment was also sequenced and a large invert repeat in the putative methionyl-tRNA synthetase promoter region was found.