Streptococcus mutans, an oral bacterium, is commonly associated with dental caries in humans. The pathogenicity of S. mutans is contributed to by multiple factors including acidogenicity, high acid and salt tolerance, biofilm formation, and high natural competence. The majority of known virulence factor proteins are secreted, cell wall-localized, membrane, or membrane-associated. Therefore, understanding the protein transport machinery of this organism is critical to fully understanding its pathogenesis. YidC belongs to a family of membrane-localized chaperone-insertases and is ubiquitously present in all three domains of life. S. mutans contains two YidC paralogues: YidC1 and YidC2. Elimination of YidC2 has strong phenotypic consequences including impaired growth, sensitivity to acid and salt, significant loss of competence, impaired cell morphology, decrease in biofilm formation, and reduced caries. I am studying the relative expression of yidC1/2 in wild-type, DyidC1 and DyidC2 strains under various growth conditions, especially the strength of the respective promoters.