Recognition of Streptococcal Promoters by the Pneumococcal SigA Protein

Virtu Solano-Collado, Sofía Ruiz-Cruz, Fabián Lorenzo-Díaz, Radoslaw Pluta, Manuel Espinosa*, Alicia Bravo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)
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Promoter recognition by RNA polymerase is a key step in the regulation of gene expression. The bacterial RNA polymerase core enzyme is a complex of five subunits that interacts transitory with one of a set of sigma factors forming the RNA polymerase holoenzyme. The sigma factor confers promoter specificity to the RNA polymerase. In the Gram-positive pathogenic bacterium Streptococcus pneumoniae, most promoters are likely recognized by SigA, a poorly studied housekeeping sigma factor. Here we present a sequence conservation analysis and show that SigA has similar protein architecture to Escherichia coli and Bacillus subtilis homologs, namely the poorly conserved N-terminal 100 residues and well-conserved rest of the protein (domains 2, 3, and 4). Further, we have purified the native (untagged) SigA protein encoded by the pneumococcal R6 strain and reconstituted an RNA polymerase holoenzyme composed of the E. coli core enzyme and the sigma factor SigA (RNAP-SigA). By in vitro transcription, we have found that RNAP-SigA was able to recognize particular promoters, not only from the pneumococcal chromosome but also from the S. agalactiae promiscuous antibiotic-resistance plasmid pMV158. Specifically, SigA was able to direct the RNA polymerase to transcribe genes involved in replication and conjugative mobilization of plasmid pMV158. Our results point to the versatility of SigA in promoter recognition and its contribution to the promiscuity of plasmid pMV158.

Original languageEnglish
Article number666504
Number of pages14
JournalFrontiers in Molecular Biosciences
Publication statusPublished - 24 Jun 2021

Bibliographical note

This study was financially supported by grants BIO2016-76412- C2-2-R (AEI/FEDER, UE) to AB from the Spanish Ministry of Economy and Competitiveness, and PID2019-104553RB-C21 to AB from the Spanish Ministry of Science and Innovation.

Thanks are due to F. W. Studier for his gift of the E. coli BL21 (DE3) strain and to L. Rodríguez for her technical help in protein purification.


  • plasmid pMV158
  • RNA polymerase
  • SigA protein
  • sigma factor
  • streptococcal promoters
  • Streptococcus pneumoniae


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