초록
<P><B>ABSTRACT</B><P> We investigated the regulation and roles of six aspartate pathway genes in l -lysine overproduction in Bacillus methanolicus : <I>dapG</I> , encoding aspartokinase I (AKI); <I>lysC</I> , encoding AKII; <I>yclM</I> , encoding AKIII; <I>asd</I> , encoding aspartate semialdehyde dehydrogenase; <I>dapA</I> , encoding dihydrodipicolinate synthase; and <I>lysA</I> , encoding <I>meso</I> -diaminopimelate decarboxylase. Analysis of the wild-type strain revealed that <I>in vivo lysC</I> transcription was repressed 5-fold by l -lysine and induced 2-fold by dl -methionine added to the growth medium. Surprisingly, <I>yclM</I> transcription was repressed 5-fold by dl -methionine, while the <I>dapG</I> , <I>asd</I> , <I>dapA</I> , and <I>lysA</I> genes were not significantly repressed by any of the aspartate pathway amino acids. We show that the l -lysine-overproducing classical B. methanolicus mutant NOA2#13A52-8A66 has-in addition to a <I>hom-1</I> mutation-chromosomal mutations in the <I>dapG</I> coding region and in the <I>lysA</I> promoter region. No mutations were found in its <I>dapA</I> , <I>lysC</I> , <I>asd</I> , and <I>yclM</I> genes. The mutant <I>dapG</I> gene product had abolished feedback inhibition by <I>meso</I> -diaminopimelate in vitro , and the <I>lysA</I> mutation was accompanied by an elevated (6-fold) <I>lysA</I> transcription level <I>in vivo</I> . Moreover, <I>yclM</I> transcription was increased 16-fold in mutant strain NOA2#13A52-8A66 compared to the wild-type strain. Overexpression of wild-type and mutant aspartate pathway genes demonstrated that all six genes are important for l -lysine overproduction as tested in shake flasks, and the effects were dependent on the genetic background tested. Coupled overexpression of up to three genes resulted in additive (above 80-fold) increased l -lysine production levels. </P></P>