Translational autoregulation of ermC 23S rRNA methyltransferase expression in Bacillus subtilis.

ermC specifies an rRNA methyltransferase that confers resistance to erythromycin. The expression of this determinant is induced by the addition of erythromycin. The induction mechanism has been shown to operate posttranscriptionally, and its mechanism has been elucidated. We now show that synthesis of the ermC gene product in Bacillus subtilis is also autoregulated by a mechanism operating on the level of translation. The synthesis of methyltransferase was shown to be gene dosage compensated by Western blot analysis. Several mutants were analyzed that specify altered ermC gene products and are deregulated. Analysis of mutants and of the wild-type strain by Northern blotting demonstrated that autoregulation is posttranscriptional. We suggest a translational repression model in which the ermC methyltransferase binds to its own mRNA, at a region that resembles the methylation target site on 23S rRNA. The overall control of ermC expression is discussed in light of these multiple regulatory mechanisms.