Abstract
The aspartase gene (aspA) of Escherichia coli K-12 was cloned on pSC101 used as a vector, by selecting transformants of an E. coli K-12 mutant unable to assimilate glutamic acid due to lack of aspartase. Plasmids pYT161 and pYT471 were constructed by inserting a 4.3 kb fragment carrying the aspA gene into pLG339, a low-copy-number vector, and into pBR322, a multicopy vector, respectively. E. coli K-12 cells harboring these plasmids produced much more aspartase than the control cells. Cells maintained pYT161 stably but did pYT471 unstably when grown in medium containing no antibiotics. The aspA product was deduced as a polypeptide of molecular weight ca. 50,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
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