title: Sequence analysis and expression of the aspartokinase and aspartate semialdehyde dehydrogenase operon from rifamycin SV-producing amycolatopsis mediterranei.
abstract: A approximately 4.8 kb KpnI fragment, from the upstream region of the methylmalonyl-CoA mutase gene (mutAB) of rifamycin SV-producing Amycolatopsis mediterranei, was cloned and partially sequenced. Codon preference analysis showed three complete ORFs. ORF2 is internal to ORF1, and encodes a polypeptide corresponding to 172 amino acids, whereas ORF1 encodes a polypeptide of 421 amino acids. They were identified as the encoding genes of aspartokinase alpha- and beta-subunits by comparing the amino acid sequences with those in the database. The downstream ORF3, whose start codon was overlapped with the stop codon of both ORF1 and ORF2 by 1 bp, was identified as the aspartate semialdehyde dehydrogenase gene (asd), encoding a polypeptide of 346 amino acids. Subclones containing either the ask gene or the asd gene were constructed, in which the genes could be expressed under Lac promoters. Two subclones could transform E. coli CGSC 5074 (ask-) and E. coli X6118 (asd-) to prototrophy, supporting the functional assignments. Southern hybridisation indicated that the approximately 4.8 kb sequenced region represented a continuous segment in the A. mediterranei chromosome. It is concluded that ask and asd genes are present in an operon in A. mediterranei, and therefore that organisation of these two genes is the same as in most gram-positive bacteria, such as Mycobacteria, Corynebacterium glutamicum and Bacillus subtilis, but is different from Streptomyces akiyoshiensis.
authors.affiliation: Department of Microbiology, Shanghai Institute of Plant Physiology, Academia Sinica, 200032 Shanghai, People's Republic of China. wzhang@hsc.vcu.edu
authors.forename: W
authors.initials: W
authors.lastname: Zhang
authors.forename: W
authors.initials: W
authors.lastname: Jiang
authors.forename: G
authors.initials: G
authors.lastname: Zhao
authors.forename: Y
authors.initials: Y
authors.lastname: Yang
authors.forename: J
authors.initials: J
authors.lastname: Chiao
mesh_terms: D039903:Actinobacteria / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D001222:Aspartate Kinase / Q000235:genetics*; D001223:Aspartate-Semialdehyde Dehydrogenase / Q000235:genetics*; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005816:Genetic Complementation Test; D008765:Methylmalonyl-CoA Mutase / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames / Q000235:genetics; D009876:Operon; D012294:Rifamycins / Q000096:biosynthesis*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D004269:DNA, Bacterial; D012294:Rifamycins; C023808:rifamycin SV; D001223:Aspartate-Semialdehyde Dehydrogenase; D001222:Aspartate Kinase; D008765:Methylmalonyl-CoA Mutase