Affiliation:
1. Section for Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, 2800 Lyngby,1 and
2. Department of Biological Chemistry, University of Copenhagen, 1307 Copenhagen,2 Denmark
Abstract
ABSTRACT
The soil bacterium
Bacillus subtilis
has developed a highly controlled system for the utilization of a diverse array of low-molecular-weight compounds as a nitrogen source when the preferred nitrogen sources, e.g., glutamate plus ammonia, are exhausted. We have identified such a system for the utilization of purines as nitrogen source in
B. subtilis
. Based on growth studies of strains with knockout mutations in genes, complemented with enzyme analysis, we could ascribe functions to 14 genes encoding enzymes or proteins of the purine degradation pathway. A functional xanthine dehydrogenase requires expression of five genes (
pucA, pucB, pucC, pucD
, and
pucE
). Uricase activity is encoded by the
pucL
and
pucM
genes, and a uric acid transport system is encoded by
pucJ
and
pucK
. Allantoinase is encoded by the
pucH
gene, and allantoin permease is encoded by the
pucI
gene. Allantoate amidohydrolase is encoded by
pucF
. In a
pucR
mutant, the level of expression was low for all genes tested, indicating that PucR is a positive regulator of
puc
gene expression. All 14 genes except
pucI
are located in a gene cluster at 284 to 285° on the chromosome and are contained in six transcription units, which are expressed when cells are grown with glutamate as the nitrogen source (limiting conditions), but not when grown on glutamate plus ammonia (excess conditions). Our data suggest that the 14 genes and the
gde
gene, encoding guanine deaminase, constitute a regulon controlled by the
pucR
gene product. Allantoic acid, allantoin, and uric acid were all found to function as effector molecules for PucR-dependent regulation of
puc
gene expression. When cells were grown in the presence of glutamate plus allantoin, a 3- to 10-fold increase in expression was seen for most of the genes. However, expression of the
pucABCDE
unit was decreased 16-fold, while expression of
pucR
was decreased 4-fold in the presence of allantoin. We have identified genes of the purine degradation pathway in
B. subtilis
and showed that their expression is subject to both general nitrogen catabolite control and pathway-specific control.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
108 articles.
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