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The aspartase gene (aspA) of Escherichia coli has been isolated in two plasmids, pGS73 and pGS94, which contain segments of bacterial DNA (12·5 and 2·8 kb, respectively) inserted into the tet gene of the vector pBR322. The plasmids were constructed by sequential sub-cloning from a larger ColEl-frd + hybrid plasmid. The location of the aspA gene confirmed predictions based on a correlation between the genetic and restriction maps of the corresponding region. The aspartase activities of plasmid-containing aspA mutants were amplified four- to sixfold relative to aspA + parental strains. The aspA gene product was tentatively identified as a poly-peptide of M r 55 000, which is somewhat larger than previous estimates (M r 45 000 to 48 000) for aspartase.
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