Molecular Characterization of the Gene Encoding the DNA Gyrase A Subunit of Streptococcus pneumoniae

The gene encoding the DNA gyrase A subunit of Streptococcus pneumoniae was cloned and sequenced. The gyrA gene codes for a protein of 822 amino acids homologous to the gyrase A subunit of eubacteria. Translation of the gene in an Escherichia coli expression system revealed a 92-kDa polypeptide. A sequence-directed DNA curvature was identified in the promoter region of gyrA. The bend center was mapped and located between the −35 and −10 regions of the promoter. Primer extension analysis showed that gyrA transcription initiates 6 bp downstream of an extended −10 promoter. The possible implications of the bent DNA region as a regulatory element in the transcription of gyrA are discussed.