Premium
A unique open reading frame within the comX gene of S treptococcus mutans regulates genetic competence and oxidative stress tolerance
Author(s) -
Kaspar Justin,
Ahn SangJoon,
Palmer Sara R.,
Choi Sang Chul,
Stanhope Michael J.,
Burne Robert A.
Publication year - 2015
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.12948
Subject(s) - biology , open reading frame , mutant , gene , genetics , regulation of gene expression , operon , peptide sequence
Summary S treptococcus mutans displays complex regulation of genetic competence, with ComX controlling late competence gene transcription. The rcrRPQ operon has been shown to link oxidative stress tolerance, (p)pp G pp metabolism and competence in S . mutans . Importantly, an rcrR polar (Δ rcrR ‐ P ) mutant is hyper‐transformable, but an rcrR non‐polar (Δ rcrR ‐ NP ) mutant cannot be transformed. Transcriptome comparisons of the rcrR mutants using RNA ‐ S eq and quantitative real‐time polymerase chain reaction revealed little expression in the 5′ region of comX in Δ rcrR ‐ NP , but high level expression in the 3′ region. Northern blotting with comX probes revealed two distinct transcripts in the Δ rcrR ‐ P and Δ rcrR ‐ NP strains, and 5′ R apid A mplification of c DNA E nds mapped the 5′ terminus of the shorter transcript to nt +140 of the comX structural gene, where a unique 69‐aa open reading frame, termed XrpA , was encoded in a different reading frame than ComX . Two single‐nucleotide substitution mutants ( comX :: T 162 C ; comX :: T 210 A ) were introduced to disrupt XrpA without affecting the sequence of ComX . When the mutations were in the Δ rcrR ‐ NP genetic background, ComX production and transformation were restored. Overexpression of xrpA led to impaired growth in aerobic conditions and decreased transformability. These results reveal an unprecedented mechanism for competence regulation and stress tolerance by a gene product encoded within the comX gene that appears unique to S . mutans .