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J. Bacteriol., Nov 1995, 6432-6439, Vol 177, No. 22
B Keuntje, B Masepohl and W Klipp
Four Rhodobacter capsulatus mutants unable to grow with proline as the sole
nitrogen source were isolated by random Tn5 mutagenesis. The Tn5 insertions
were mapped within two adjacent chromosomal EcoRI fragments. DNA sequence
analysis of this region revealed three open reading frames designated selD,
putR, and putA. The putA gene codes for a protein of 1,127 amino acid
residues which is homologous to PutA of Salmonella typhimurium and
Escherichia coli. The central part of R. capsulatus PutA showed homology to
proline dehydrogenase of Saccharomyces cerevisiae (Put1) and Drosophila
melanogaster (SlgA). The C-terminal part of PutA exhibited homology to Put2
(pyrroline-5-carboxylate dehydrogenase) of S. cerevisiae and to aldehyde
dehydrogenases from different organisms. Therefore, it seems likely that in
R. capsulatus, as in enteric bacteria, both enzymatic steps for proline
degradation are catalyzed by a single polypeptide (PutA). The deduced amino
acid sequence of PutR (154 amino acid residues) showed homology to the
small regulatory proteins Lrp, BkdR, and AsnC. The putR gene, which is
divergently transcribed from putA, is essential for proline utilization and
codes for an activator of putA expression. The expression of putA was
induced by proline and was not affected by ammonia or other amino acids. In
addition, putA expression was autoregulated by PutA itself. Mutations in
glnB, nifR1 (ntrC), and NifR4 (ntrA encoding sigma 54) had no influence on
put gene expression. The open reading frame located downstream of R.
capsulatus putR exhibited strong homology to the E. coli selD gene, which
is involved in selenium metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Expression of the putA gene encoding proline dehydrogenase from Rhodobacter capsulatus is independent of NtrC regulation but requires an Lrp-like activator protein
Lehrstuhl fur Genetik, Fakultat fur Biologie, Universitat Bielefeld, Germany.
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