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Journal of Bacteriology, November 2001, p. 6197-6206, Vol. 183, No. 21
Departamento de Biotecnología
Microbiana, Centro Nacional de Biotecnología, CSIC, Campus de
la Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid,
Spain
Received 11 June 2001/Accepted 25 July 2001
Expression of the alkane degradation pathway encoded in the OCT
plasmid of Pseudomonas putida GPo1 is induced in the
presence of alkanes by the AlkS regulator, and it is down-regulated by catabolic repression. The catabolic repression effect reduces the expression of the two AlkS-activated promoters of the pathway, named PalkB and PalkS2. The P.
putida Crc protein participates in catabolic repression of some
metabolic pathways for sugars and nitrogenated compounds. Here, we show
that Crc has an important role in the catabolic repression exerted on
the P. putida GPo1 alkane degradation pathway when cells
grow exponentially in a rich medium. Interestingly, Crc plays little or
no role on the catabolic repression exerted by some organic acids in a
defined medium, which shows that these two types of catabolic
repression can be genetically distinguished. Disruption of the
crc gene led to a six- to sevenfold increase in the
levels of the mRNAs arising from the AlkS-activated
PalkB and PalkS2 promoters in cells
growing exponentially in rich medium. This was not due to an increase in the half-lives of these mRNAs. Since AlkS activates the expression of its own gene and seems to be present in limiting amounts, the higher
mRNA levels observed in the absence of Crc could arise from an increase
in either transcription initiation or in the translation efficiency of
the alkS mRNA. Both alternatives would lead to increased
AlkS levels and hence to elevated expression of PalkB
and PalkS2. High expression of alkS from
a heterologous promoter eliminated catabolic repression. Our results
indicate that catabolic repression in rich medium is directed to
down-regulate the levels of the AlkS activator. Crc would thus
modulate, directly or indirectly, the levels of AlkS.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.21.6197-6206.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Role of the crc Gene in Catabolic
Repression of the Pseudomonas putida GPo1 Alkane
Degradation Pathway
*
Corresponding author. Mailing address: Centro Nacional
de Biotecnología, CSIC, Campus de la Universidad Autónoma
de Madrid, Cantoblanco, 28049 Madrid, Spain. Phone: (34) 91 585 45 39. Fax: (34) 91 585 45 06. E-mail: frojo{at}cnb.uam.es.
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