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J. Bacteriol., Apr 1995, 1981-1988, Vol 177, No. 8
KR Gutshall, DE Trimbur, JJ Kasmir and JE Brenchley
We have characterized a new psychrotrophic Arthrobacter isolate which
produces beta-galactosidase isozymes. When DNA from this isolate was
transformed into an Escherichia coli host, we obtained three different
fragments, designated 12, 14, and 15, each encoding a different beta-
galactosidase isozyme. The beta-galactosidase produced from fragment 12 was
of special interest because the protein subunit was smaller (about 71
versus 116 kDa) than those typically encoded by the lacZ family. The
isozyme encoded by fragment 12 was purified, and its activity and
thermostability were examined. Although the enzyme is highly specific
towards beta-D-galactoside substrates, its levels in the isolate do not
increase in cells grown with lactose. Nucleotide sequence determination
showed that the gene encoding isozyme 12 is not similar to the other
members of the lacZ family but has regions similar to beta- galactosidase
isozymes from Bacillus stearothermophilus and B. circulans. Addition of the
isozyme 12 sequence to the database made it possible to examine these
enzymes as possible members of a new, separate family. Our analysis of this
new family showed some conserved amino acids corresponding to the lacZ
acid-base catalytic region but no homology with the nucleophilic region. On
the basis of these comparisons, we designated this a new lacG family.
Copyright © 1995, American Society for Microbiology
Analysis of a novel gene and beta-galactosidase isozyme from a psychrotrophic Arthrobacter isolate
Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, USA.
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