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Biotechnology |
Institute of Genetics and Selection of Industrial Micro-organisms, 1st-Dorozhniy pr. 1, Moscow, Russia1
Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794-5000, USA2
Author for correspondence: George N. Marchenko. Tel: +1 516 632 9233. Fax: +1 516 632 8820. e-mail: gmarchenko{at}ccmail.sunysb.edu
The genes encoding aspartate kinase (ask), homoserine dehydrogenase (hom), homoserine kinase (thrB) and threonine synthase (thrC) from the obligate methylotroph Methylobacillus flagellatus were cloned. In maxicells hom and thrC directed synthesis of 51 and 48 kDa polypeptides, respectively. The hom, thrB and thrC genes and adjacent DNA areas were sequenced. Of the threonine biosynthesis genes, only hom and thrC were tightly linked in the order hom-thrC. The gene for thymidylate synthase (thyA) followed thrC and the gene for aspartate aminotransferase (aspC) preceded hom. All four genes (aspC-hom-thrC-thyA) were transcribed in the same direction. mRNA analysis indicated that hom-thrC are apparently transcribed in one 7·5 kb transcript in M. flagellatus. Promoter analysis showed the presence of a functional promoter between aspC and hom. No functional promoter was found to be associated with the DNA stretch between hom and thrC. The thrB gene encoded an unusual type of homoserine kinase and was not linked to other threonine biosynthesis genes.
Keywords: Methylobacillus flagellatus, threonine biosynthesis, homoserine dehydrogenase, homoserine kinase, threonine synthase
Abbreviations: ASD, aspartate semialdehyde dehydrogenase; ASK, aspartate kinase; HDH, homoserine dehydrogenase; HK, homoserine kinase; TS, threonine synthase
The GenBank accession numbers for the aspC-hom-thrC-thyA gene cluster and thrB gene sequences from M. flagellatus reported in this paper are L78665 and L78666, respectively.
a Present address: Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794-5000, USA.
b Present address: Department of Pathology, State University of New York at Stony Brook Medical Center, Stony Brook, NY 11794-8691, USA.
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