Abstract
Proteins belonging to the LraI (for “lipoprotein receptor antigen”) family function as adhesins in several streptococci, as a virulence factor for endocarditis in at least one of these species, and potentially as metal transporters in many bacteria. We have identified and characterized the chromosomal locus containing the LraI family gene (designated
sloC
) from
Streptococcus mutans
, an agent of dental caries and endocarditis in humans. Northern blot analysis indicated that
sloC
is cotranscribed with three other genes. As with other LraI operons, the
sloA
and
sloB
genes apparently encode components of an ATP-binding cassette transport system. The product of the fourth gene,
sloR
, has homology to the metal-dependent regulator from
Corynebacterium diphtheriae
, DtxR. A potential binding site for SloR was identified upstream from the
sloABCR
operon and was conserved upstream from LraI operons in several other streptococci. Potential SloR homologs were identified in the unfinished genomic sequences from two of these,
S. pneumoniae
and
S. pyogenes
. Mutagenesis of
sloC
in
S. mutans
resulted in apparent loss of expression of the entire operon as assessed by Northern blot analysis. The
sloC
mutant was indistinguishable from its wild-type parent in a gnotobiotic rat model of caries but was significantly less virulent in a rat model of endocarditis. Virulence for endocarditis was restored by correction of the
sloC
mutation but not by provision of the
sloC
gene in
trans
, suggesting that virulence requires the expression of other genes in the
sloC
operon.
