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J. Bacteriol., Mar 1995, 1307-1314, Vol 177, No. 5
AS Paradkar and SE Jensen
A Streptomyces clavuligerus mutant disrupted in cas2, encoding the
clavaminate synthase (CAS2) isoenzyme, was constructed by a gene
replacement procedure. The resulting cas2 mutant showed no clavulanic acid
production when grown in starch-asparagine medium. However, in soy medium,
the cas2 mutant did produce clavulanic acid, although in amounts less than
those produced by wild-type cultures. This medium- dependent leaky
phenotype correlated well with the presence of the cas1 transcript,
encoding the CAS1 isoenzyme, in cultures grown in soy medium and with its
absence from those grown in starch-asparagine medium. This suggested that
CAS1 and CAS2 both contribute to clavulanic acid production but that their
production is regulated differently. Under nutritional conditions in which
cas1 expression is blocked, cas2 becomes essential for clavulanic acid
production. Northern (RNA) analysis revealed that while cas1 is transcribed
as a 1.4-kb monocistronic transcript only, cas2 is transcribed both as a
1.2-kb monocistronic transcript and as part of a 5.3-kb polycistronic
transcript. High-resolution S1 nuclease analysis located the transcription
start point of the monocistronic cas2 transcript at a C residue 103
nucleotides upstream from the cas2 start codon.
Copyright © 1995, American Society for Microbiology
Functional analysis of the gene encoding the clavaminate synthase 2 isoenzyme involved in clavulanic acid biosynthesis in Streptomyces clavuligerus
Department of Biological Sciences, University of Alberta, Edmonton, Canada.
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