Affiliation:
1. Department of Molecular Microbiology, John Innes Centre, Colney, Norwich NR4 7UH, United Kingdom
Abstract
ABSTRACT
Sporulation mutants of
Streptomyces coelicolor
appear white because they are defective in the synthesis of the gray polyketide spore pigment, and such white (
whi
) mutants have been used to define 13 sporulation loci.
whiN
, one of five new
whi
loci identified in a recent screen of NTG (
N
-methyl-
N
′-nitro-
N
-nitrosoguanidine)-induced
whi
strains (N. J. Ryding et al., J. Bacteriol. 181:5419–5425, 1999), was defined by two mutants, R112 and R650. R650 produced frequent spores that were longer than those of the wild type. In contrast, R112 produced long, straight, undifferentiated hyphae, although rare spore chains were observed, sometimes showing highly irregular septum placement. Subcloning and sequencing showed that
whiN
encodes a member of the extracytoplasmic function subfamily of RNA polymerase sigma factors and that the sigma factor has an unusual N-terminal extension of approximately 86 residues that is not present in other sigma factors. A constructed
whiN
null mutant failed to form aerial mycelium (the “bald” phenotype) and, as a consequence,
whiN
was renamed
bldN
. This observation was not totally unexpected because, on some media, the R112 point mutant produced substantially less aerial mycelium than its parent, M145. The
bldN
null mutant did not fit simply into the extracellular signaling cascade proposed for
S. coelicolor bld
mutants. Expression of
bldN
was analyzed during colony development in wild-type and aerial mycelium-deficient
bld
strains.
bldN
was transcribed from a single promoter,
bldNp. bldN
transcription was developmentally regulated, commencing approximately at the time of aerial mycelium formation, and depended on
bldG
and
bldH
, but not on
bldA
,
bldB
,
bldC
,
bldF
,
bldK
, or
bldJ
or on
bldN
itself. Transcription from the
p1
promoter of the response-regulator gene
bldM
depended on
bldN
in vivo, and the
bldMp1
promoter was shown to be a direct biochemical target for ς
BldN
holoenzyme in vitro.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
128 articles.
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