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標題: Molecular genetic analyses of potential beta-galactosidase genes in Xanthomonas camplestris
作者: Yang, T.C.
Hu, R.M.
Hsiao, Y.M.
Weng, S.F.
Tseng, Y.H.
關鍵字: beta-galactosidase;Xanthomonas campestris;glycosyl hydrolase;acid-sequence similarities;phage-phi-lf;xanthan gum;glycosyl;hydrolases;streptococcus-pneumoniae;campestris strain;genome;sequence;lactose;cloning;dna
Project: Journal of Molecular Microbiology and Biotechnology
期刊/報告no:: Journal of Molecular Microbiology and Biotechnology, Volume 6, Issue 3-4, Page(s) 145-154.
Xanthomonas campestris pv. campestris, which displays no significant beta-1,4-agalactopyranosidase activity, has three annotated beta-galactosidase genes in the sequenced genome, designated galA, galB and galC herein. GalA and GalB are similar to glycosyl hydrolase (GH) family 2 enzymes, including Escherichia coli LacZ. galA and galB cannot express detectable activity even after being cloned in-frame and driven by the vector's promoter. GalC is a GH35 enzyme homologous to the Xanthomonas axonopodis pv. manihotis Bga. The latter cleaves beta,1-3-linked galactose 1,000 times faster than beta,1-4-linked galactose and is not responsible for lactose utilization. In X campestris pv. campestris cells, GalC is readily detectable by Western blotting, and the levels can be increased by cloning the gene under the control of the vector's promoter. Results of insertional mutation, transcriptional fusion assay and Western blotting indicated that galC, clustered with several GH genes, is cotranscribed with the upstream gene(s) and is expressed constitutively. Xc17L is a previously isolated mutant with elevated beta-galactosidase activity and a greatly improved ability to grow on lactose. Results of DNA sequencing of Xc17L galA, galB and galC, enzyme assays of galA, galB and galC mutants derived from Xc17L, and Western blotting of GalC in Xc17L indicated that the three beta-galactosidase genes do not encode the elevated P-galactosidase activity in Xc17L. The presence of a fourth beta-galactosidase gene is proposed. Copyright (C) 2003 S. Karger AG, Basel.
ISSN: 1464-1801
DOI: 10.1159/000077245
Appears in Collections:分子生物學研究所

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