Rgg is a positive transcriptional regulator of the Streptococcus gordonii gtfG gene

Abstract

The Streptococcus gordonii (Challis) glucosyltransferase-encoding determinant gtfG is regulated by the product of the adjacent gene rgg. Results of analyses described here showed that in both S. gordonii and Escherichia coli Rgg is a positive transcriptional regulator of glucosyltransferase expression. In addition, the transcriptional start sites of both gtfG and rgg were determined.Glucosyltransferases (GTFs) are enzymes that polymerize the glucose moiety of sucrose to yield glucan. The enzymes are thought to be important for the mutans streptococci in sucrosedependent bacterial accumulation on smooth tooth surfaces (9). The production of glucan by Streptococcus gordonii has been correlated with the accumulation of this organism on hydroxyapatite beads (24); thus, GTF may play a role in the colonization of S. gordonii on the tooth surface. Experimental evidence also suggests that this enzyme may be a virulence factor for S. gordonii in the pathogenesis of infective endocarditis (12, 16), although a recent report suggests that this is not the case for S. gordonii Challis, at least in a rat endocarditis model (26).The complete nucleotide sequence of S. gordonii Challis gtfG was determined recently (25), and the corresponding protein had a mass of ca. 170 kDa. We previously identified a gene, rgg, located immediately upstream of gtfG, that functions as a positive regulator of GTF expression (21). Haisman and Jenkinson have also identified two distinct genetic regulatory loci, gtf-20 and gtf-30, that appear to regulate GTF expression (4). Here, we report the results of Northern (RNA) blot and primer extension analyses of the rgg-gtfG locus, which show (i) transcripts that are expressed at the rgg and gtfG loci and where they are initiated and (ii) that the rgg product affects GTF expression at the level of transcription. In addition, our conclusions are corroborated by the demonstration of regulation of gtfG in Escherichia coli with a gtfGЈ-lacZ transcriptional reporter fusion.A restriction endonuclease map of the rgg-gtfG region of the S. gordonii Challis chromosome, related probes used for Northern hybridization, and sizes and locations of transcripts detected are shown in Fig. 1A. Several mRNA transcripts were identified in the strain containing the streptococcal cloning vector pVA749 (Fig. 1B, lanes 4). A 1.7-kb band was identified with the upstream probe. A 1.1-kb band was identified exclusively with the rgg probe, a 5.4-kb band only was identified with the gtfG probe, and a 6.4-kb band was identified with both the rgg and gtfG probes. The data are consistent with the following three transcripts derived from the rgg and gtfG loci (Fig. 1A): (i) a 1.1-kb rgg transcript, large enough to contain the rgg open reading frame (ORF) of 891 nucleotides; (ii) a 5.4-kb gtfG transcript that is of a size sufficient to contain the entire structural determinant of the GTF (22, 25); and (iii) a 6.4-kb rgggtfG transcript that likely represents a transcript originating at the rgg promoter and terminating at the same site as the...

Characterization of the Streptococcus gordonii chromosomal region immediately downstream of the glucosyltransferase gene

“…(a) gtfG-probed RNA of strains CH1, CH8942 and CH8961 indicates that the levels of the 5n4 kb gtfG-specific and the 6n4 kb rgg/gtfG polycistronic transcripts are similar in all three strains. The lower levels of polycistronic transcript compared with gtfG-specific transcript are consistent with previously published results (Sulavik & Clewell, 1996). (b) rggD-probed RNA of strains CH1, CH1(pMI226), CH1(pVA749) demonstrates the " 1 kb rggD transcript.…”

“…There is an increase in the quantity and size of transcripts in the strain carrying plasmid-borne rggD, which may be due to readthrough in the multicopy pVA749 vector. This has been noted for pAMS57, by Sulavik & Clewell (1996). (c) dsg-probed RNA of strains CH1, CH1(pMI226) and CH8961 shows similar amounts of the " 1n3 kb dsg-specific transcript.…”

“…Both rgg and gtfG have their own putative promoter and ribosome-binding site. Three mRNA transcripts have been associated with the rgg\gtfG locus : a 1n1 kb rgg-specific transcript, a 5n5 kb gtfG-specific transcript and a 6n5 kb rgg\gtfG polycistronic transcript (Sulavik & Clewell, 1996).…”

Tales of conjugation and sex pheromones

“…164 We eventually identified the GTF gene (gtfG) as well as an adjacent upstream gene encoding a novel positive transcriptional regulator Rgg. [165][166][167] The Rgg find turned out to be quite significant as homologues are now widely found among most Gram-positive bacteria, some of which regulate virulence; and it has been suggested recently by Mashburn-Warren et al 168 that Rgg-like proteins in general relate to regulation of activities that reflect population densities and peptide production. Indeed, they appear to be part of a superfamily of proteins that bind cytoplasmic signals, which, amazingly, includes the pheromonebinding PrgX protein (a pAD1 TraA homologue) related to the E. faecalis pCF10 system.…”

Responses of Cariogenic Streptococci to Environmental Stresses

“…gordonii (Sulavik and Clewell, 1996), and to regulate expression of several exo-proteins that are preferentially expressed during stationary phase growth in S. pyogenes (Chaussee et al, 2001).…”