Cloning and expression of an Arabidopsis thaliana cDNA encoding a monofunctional aspartate kinase homologous to the lysine-sensitive enzyme of Escherichia coli.

摘要

As in many bacterial species, the first enzymatic reaction of the aspartate-family pathway in plants is mediated by several isozymes of aspartate kinase (AK) that are subject to feedback inhibition by the end-product amino acids lysine or threonine.So far, only cDNAs and genes encoding threonine-sensitive AKs have been cloned from plants. These were all shown to encode polypeptides containing two linked activities, namely AK and homoserine dehydrogenase (HSD), similar to the E. coli thrA gene encoding a threonine-sensitive bifunctional AK/HSD isozyme. This paper describes the cloning of a new A. thaliana cDNA that is relatively highly homologous to the E. coli lysC gene encoding the lysine-sensitive AK isozyme. Moreover, similar to the bacteriallysine-sensitive AK, the polypeptide encoded by the present cDNA is monofunctional and does not contain an HSD domain. These observations imply that this cloned cDNA encodes a lysine-sensitive AK. Southern blot hybridization detected a single gene highlyhomologous to the present cDNA, plus an additional much less homologous gene. This was confirmed by the independent cloning of an additional Arabidopsis cDNA encoding a lysine-sensitive AK. Northern blot analysis suggested that the gene encoding this monofunctional AK cDNA is abundantly expressed in most if not all tissues of Arabidopsis. Nucleotide sequence data have been submitted to the EMBL/GenBank/DDBJ databases under the accession number U62020.