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摘要
The gene encoding a beta-galactosidase from Xanthomonas manihotis was cloned into Escherichia coli, The gene resides on a 2.4 kb DNA fragment which was isolated from a partial Sau3A library in the cloning vector pUC19 using 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal) as the selection. The enzyme produced by the clone has a specificity for beta 1-3- > beta 1-4-linked galactose, The nucleotide sequence of the gene was determined, The deduced protein sequence contained 597 amino acids yielding a monomeric molecular mass of 66 kDa, The cloned beta-galactosidase showed no similarity to any known prokaryotic beta-galactosidase. However, extensive similarity was observed with eukaryotic beta-galactosidases from animals, plants and fungi, The strongest similarity was with the beta-galactosidases found in the human and mouse lysosomes (42 and 41% identity, respectively), Alignment of the X.manihotis and eukaryotic beta-galactosidase sequences revealed seven highly conserved domains common to each protein, Additionally, Domain 1 in X.manihotis showed similarity to regions within catalytic domains from seven xylanases and cellulases belonging to family 10 of glucosyl hydrolases. A region spanning Domain 2 showed similarity to the catalytic domain of endo beta 1-3 glucanases from tobacco and barley.
- 出版日期1995-9
- 单位New England Biolabs
