Methods: Analysis of the complete genome of S. mutans UA159 in the Oralgen database (http://oralgen.lanl.gov/oralgen-tng/) indicated the nrgA gene as a possible S. mutans ammonium transporter and glnB, located upstream of the nrgA gene, as a member of the PII protein superfamily. In this study, we analyzed the nrgA gene of S. mutans strain MT8148 (serotype c). To specify the functioning unit or operon of nrgA, northern blotting and PCR analyses were performed, while we also examined expression of the nrgA gene under the influence of 2 mM glutamine using real-time quantitative reverse transcription (RT)-PCR.
Results: Northern blot analysis for determination of transcriptional organization of the nrgA gene locus revealed a positive band, estimated to be 1600 bp. The length of the transcription was matched to the length of the nrgA and glnB genes. Furthermore, PCR analysis confirmed that the band was located in the intergenic region between the nrgA and glnB genes. RT-PCR results also revealed that nrgA gene expression was elevated in the presence of 2 mM glutamine as compared to in its absence.
Conclusions: The nrgA gene of S. mutans may have a strong relationship with its ammonium transporter. Furthermore, it is transcribed with the glnB gene, with a possible predicted function of nitrogen regulatory protein PII.