Identification of the truncated transcript from the Streptococcus mutans bglP locus in the absence of esculin

Objectives: To understand the transcriptional regulation of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) of Streptococcus mutans, which is the primary causative agent of dental caries and has been associated with septic endocarditis. Carbohydrate metabolism is key in the pathogenic process. S. mutans relies on the PTS for the translocation of carbohydrates into the cell for subsequent utilization. The PTS contains carbohydrate-specific components that are responsible for the transport of various carbohydrates, including the beta-glucoside esculin. A PTS regulon responsible for esculin utilization in the presence of glucose has been isolated from S. mutans. The bglP gene encodes the PTS enzyme II permease involved with transport of esculin into the cell. Methods: Transcriptional analysis of the bglP promoter region has indicated that the gene is induced by esculin, even in the presence of glucose. Results: The bglP promoter activity has been localized to a region that contains a putative –35 sequence (TTGCAA) and a putative –10 sequence (TATAAT). The transcriptional start site has been identified by primer extension. The licT gene, located 5’ to the bglP gene, has been shown to encode an antiterminator protein that positively regulates the expression level of the bglP gene. The LicT protein appears to bind to a ribonucleic antitermination (RAT) site within the mRNA, which prevents the formation of a terminator structure that would block transcription of the bglP gene. Data obtained from transcript mapping experiments support this hypothesis. A 109 bp transcript has been identified as the terminated bglP transcript that is produced in the absence of esculin. This short transcript contains both the sequence for the RAT site as well as the sequence encoding a potential terminator structure. Conclusions: This data combined with transcriptional activity data supports the idea that transcriptional antitermination is a major regulatory mechanism involved with esculin transport by the bglP locus in S. mutans.