Affiliation:
1. School of Biomolecular and Biomedical Science and Conway Institute, University College Dublin, Dublin 4, Ireland
Abstract
ABSTRACT
The
virR
operon, located on the virulence plasmid of the intracellular pathogen
Rhodococcus equi
, contains five genes, two of which (
virR
and
orf8
) encode transcriptional regulators. The first gene of the operon (
virR
), encoding a LysR-type transcriptional regulator, is transcribed at a constitutive low level, whereas the four downstream genes are induced by low pH and high growth temperature. Differential regulation of the
virR
operon genes could not be explained by differential mRNA stability, as there were no major differences in mRNA half-lives of the transcripts representing each of the five genes within the
virR
operon. Transcription of
virR
is driven by the P
virR
promoter, with a transcription start site 53 bp upstream of the
virR
initiation codon. The four genes downstream of
virR
are transcribed from P
virR
and from a second promoter, P
orf5
, located 585 bp downstream of the
virR
initiation codon. VirR binds to a site overlapping the initiation codon of
virR
, resulting in negative autoregulation of the
virR
gene, explaining its low constitutive transcription level. The P
orf5
promoter is induced by high temperature and low pH, thus explaining the observed differential gene expression of the
virR
operon. VirR has a positive effect on P
orf5
activity, whereas the response regulator encoded by
orf8
is not involved in regulating transcription of the
virR
operon. The P
virR
promoter is strikingly similar to those recognized by the principal sigma factors of
Streptomyces
and
Mycobacterium
, whereas the P
orf5
promoter does not share sequence similarity with P
virR
. This suggests that P
orf5
is recognized by an alternative sigma factor.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
39 articles.
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