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

Abstract

The Streptococcus gordonii glucosyltransferase gene, gtfG, is positively regulated by the upstream determinant rgg. In the present study, two ORFs, transcribed on the opposite DNA strand, were identified immediately downstream of gtfG. The first, designated dsg, shares a convergent putative transcriptional terminator with gtfG, and encodes a predicted 46 kDa transmembrane protein similar to the Yersinia enterocolitica TrsA involved in polysaccharide biosynthesis. Insertional inactivation of dsg resulted in only " " 60 % of the parental level of glucosyltransferase activity. The 870 bp gene 5' to dsg is similar to the gtfG regulatory determinant. Designated rggD, this rgglike determinant downstream of gtfG encodes a putative 336 kDa cytoplasmic protein. Despite their sequence similarity, the functions of rgg and rggD appear specific. Strains in which rggD was insertionally inactivated and strains containing plasmid-borne rggD had parental levels of glucosyltransferase activity. Northern blot hybridization analyses showed " 13 kb dsg-specific and " 10 kb rggD-specific mRNA transcripts associated with this region ; no polycistronic transcript was observed. Although rgg-like gene products have been demonstrated to function as positive transcriptional regulators of adjacent genes in several streptococcal species, Northern blot analysis suggested that rggD did not influence the transcription of dsg or the divergent downstream ylbN-like determinant under the conditions in the present study. Comparison of this S. gordonii chromosome region to other streptococcal genomes, which do not contain the rgg/rggD-flanked region involved in glucan synthesis, raised intriguing possibilities about the origins of this chromosomal region, and also suggested that rggD might regulate a distally located gene.

Genetic Analysis of the rgg-gtfG Junctional Region and Its Role in Streptococcus gordonii Glucosyltransferase Activity

“…Computer analysis (3) of these encoded Rgg-like proteins (38) indicates that despite their varied target genes, they share a similar helix-turn-helix motif with potential DNA binding function (39). Comparison of these characterized rgg-like gene sequences using Clustal analysis (29) indicates that despite overall homology, the 3Ј ends of these genes and the carboxyl-terminal regions of their encoded proteins are less conserved (38). This suggests that functional specificity of Rgglike proteins may involve amino acids in this region.…”

“…gordonii (12,38). Genes with similarity to rgg have also been described in Streptococcus sanguis, Streptococcus oralis, (33,9) and Lactococcus lactis (23).…”

The Rgg Regulator of Streptococcus pyogenes Influences Utilization of Nonglucose Carbohydrates, Prophage Induction, and Expression of the NAD-Glycohydrolase Virulence Operon

“…Orthologues have not been identified for Staphylococci, Bacillus, or gram-negative bacteria. Rgg-like proteins have a putative helix-turn-helix motif, which is likely to facilitate binding to the promoter regions of Rgg-regulated genes (19,25,27,34). The first member to be characterized was designated Rgg because it is a positive regulator of the adjacent glucosyltransferase G gene (gtfG) in S. gordonii; GtfG catalyzes the formation of extracellular glucans (30,31).…”

Contribution of Invariant Residues to the Function of Rgg Family Transcription Regulators

“…This group is widely distributed, and the members occur in both pathogenic and commensal species and include Rgg of Streptococcus gordonii, which is required for extracellular glucosyltransferase expression (29,30); GadR of Lactococcus lactis, which is required for glutamate-dependent acid tolerance (27); MutR, which is required for expression of the mutacin lantibiotic, MutA, of Streptococcus mutans (23); and the plasmid-encoded LasX protein of Lactobacillus sakei, which regulates the synthesis of and immunity to the lantibiotic lactocin S (25,28). Additional uncharacterized Rgg-like proteins are encoded by the genomes of Streptococcus pneumoniae (31), Streptococcus agalactiae (13), Streptococcus oralis (10), Streptococcus sanguis (34), Streptococcus equi (http://www.sanger.ac.uk), and Listeria monocytogenes (12), and some genomes, like those of S. pyogenes (9), S. gordonii (15,33), S. pneumoniae (31), and S. mutans (1), contain multiple rgg-like genes.…”