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Interruption of the Streptococcus gordonii M5 sspA/sspB intergenic region by an insertion sequence related to IS1167
Donald R Demuth1, Yang Duan1, Howard F Jenkinson2
1Department of Biochemistry, University of Pennsylvania, School of Dental Medicine, Philadelphia, Pennsylvania 19104-6002, USA.
Abstract:
Streptococcus gordonii M5 and DL1 each express two related adhesin polypeptides, SspA and SspB, which are members of the antigen I/II family of streptococcal surface proteins. The sspA and sspB genes are tandemly arranged in both strains, with sspA residing upstream of sspB. The genes are separated by approximately 400 nucleotides in S. gordonii DL1 and 1300 nucleotides in S. gordonii M5. The nucleotide sequence of the sspA/sspB intergenic region of strain M5 is reported and the difference in length compared to S. gordonii DL1 shown to arise from the presence of an insertion sequence, designated ISSg1, consisting of 1197 bp. The nucleotide sequence of ISSg1 is highly homologous to IS1167 to Streptococcus pneumoniae and is related to a lesser extent to other members of the IS1096 family of bacterial insertion sequences. It contains a single ORF of 1026 bp, encoding a putative transposase polypeptide of 342 amino acids. The deduced transposase sequence exhibits 93% identity with the transposase polypeptides encoded by IS1167. However, the S. gordonii protein lacks a 90 residue central domain that is present in the IS1167 transposase and in the transposase polypeptides encoded by the related IS elements. In addition, the organization of the inverted repeats flanking the transposase gene in S. gordonii differs from IS1167. Extension products generated from a sspB-specific primer indicated that transcription initiates within the intergenic region in both S-gordonii strains, suggesting that sspA and sspB are independently transcribed. Transcription appears to initiate 42 bases upstream of sspB in S. gordonii DL1. In contrast, sspB transcription in M5 initiates at least 125 bases upstream of sspB, in close proximity to the terminal inverted repeat of ISsg1. These results indicate that the sspB promoter of S. gordonii M5 and DL1 are not conserved and suggest that ISSg1 sequences may play a role in directing the expression of sspB in S. gordonii M5.
Insights
Streptococcus gordonii strains M5 and DL1 possess distinct intergenic regions between sspA and sspB genes due to an insertion sequence (ISSg1) in M5. This insertion influences sspB gene transcription initiation and regulation.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus gordonii expresses adhesins SspA and SspB, crucial for cell surface interactions.
- These adhesins are encoded by tandemly arranged sspA and sspB genes in both M5 and DL1 strains.
- Gene arrangement and intergenic regions can significantly impact gene expression.
Purpose of the Study:
- To characterize the sspA/sspB intergenic region in Streptococcus gordonii M5.
- To investigate the structural and functional differences in the intergenic regions between S. gordonii M5 and DL1.
- To determine the role of the intergenic region and insertion sequences in regulating sspB gene expression.
Main Methods:
- Nucleotide sequencing of the sspA/sspB intergenic region in S. gordonii M5.
- Comparative sequence analysis with S. gordonii DL1 and related insertion sequences.
- Identification and characterization of insertion sequence ISSg1.
- Transcriptional analysis using primer extension to identify transcription start sites.
Main Results:
- The intergenic region of S. gordonii M5 is longer than DL1 due to a 1197 bp insertion sequence, ISSg1.
- ISSg1 shares homology with IS1167 from Streptococcus pneumoniae and contains a transposase gene, but with variations.
- Transcription of sspB initiates differently in M5 and DL1, with M5 initiation occurring near the ISSg1 terminal repeat, suggesting ISSg1 influences promoter activity.
Conclusions:
- The sspA/sspB intergenic region structure varies between S. gordonii strains M5 and DL1 due to ISSg1.
- ISSg1 insertion in S. gordonii M5 alters the sspB promoter region.
- ISSg1 likely plays a role in regulating sspB gene expression in S. gordonii M5.