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J. Mol. Micro. Biotechnol. 3: 95-101
A s-Like Factor Responsible for Carotenoid Biosynthesis in Streptomyces griseus
Han-Seung Lee, Yasuo Ohnishi and Sueharu Horinouchi
Self-cloning experiments with a high-copy-number plasmid and
Streptomyces griseus IFO13350 led to the cloning of a 11-kb DNA fragment that conferred
yellow pigment production on the host. The cloned fragment contained a gene cluster for carotenoid biosynthesis, in which two polycistrons,
crtE (encoding geranylgeranyl pyrophosphate
synthase)-crtI (phytoene
dehydrogenase)-crtB (phytoene
synthase)-crtV (functionally unknown methyltransferase-like protein) and
crtY (lycopene cyclase)-crtT (functionally unknown methyltransferase-like
protein)-crtU (b-carotene dehydrogenase), were present in a convergent way. Since strain IFO13350
produced no detectable amount of carotenoids, an increase in the copy number of the
crt gene cluster led to production of carotenoids at a detectable level. Overexpression
of the stress-responsive sB-like protein CrtS from
Streptomyces setonii also activated the cryptic
crt genes in S. griseus and conferred pigmentation. A CrtS
homologue (sCrtS) in S. griseus, which was predicted by a computer-aided homology search, caused carotenogenesis to the same extent as CrtS of
S. setonii, indicating that the two
sB-like proteins were functionally the same. Yellow pigment production by
S. griseus containing crtS under the control of a strong promoter on a
high-copy-number plasmid resulted from activation of transcription of the
crt genes, because overexpression of
sCrtS in S. griseus led to transcriptional activation of
the promoters in front of crtE and
crtY. S1 nuclease mapping showed that
crtS itself was transcribed at a low level under the laboratory conditions, which may account
for undetectable production of carotenoids. The
crt genes were suggested to locate very near one end of the linear chromosome, since they were completely deleted
in mutant HH1 having large deletions at both ends. The gene organization of
crt in S. griseus is similar to that in
S. coelicolor A3(2) where the whole crt
gene set is near one end of the chromosome.
Full article [pdf]
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