Bacterial small RNAs (sRNAs) are important regulators of gene expression; however, the impact of natural mutations on sRNA functions has not been studied extensively. Here we show that the sRNA MgrR contains a unique 53 bp insertion in , a close relative of and . The insertion is a repetitive extragenic palindromic (REP) sequence that could block transcription, but full-length MgrR is produced in , showing that the insertion has not affected sRNA production. Additionally, despite containing the large insertion, the sRNA appears to be functional because deletion of made more susceptible to HO. The molecular details of MgrR's roles in HOdefence are yet to be defined, but our results suggest that having an alternative function allowed the sRNA to be retained in despite it sustaining a large, potentially disruptive mutation.
