MOLECULAR CHARACTERIZATION AND EXPRESSION ANALYSIS OF THE SUPEROXIDE-DISMUTASE GENE FROM STREPTOCOCCUS-AGALACTIAE

We have cloned and sequenced a 3103-bp DNA fragment carrying the gene encoding the Mn-SOD from Streptococcus agalactiae NEM318 serotype III. This DNA fragment contained four orfs that have the same polarity of transcription. Orf1 was truncated by molecular cloning and the corresp onding 228-aa-long polypeptide did not exhibit any significant homolog y with other cognate proteins. Orf2 encodes a protein of 345 aa that d isplays some similarity (29% identity) with the YqeN peptide of Bacill us subtilis, the function of which is unknown. Orf3 encodes the 202-aa -long Mn-SOD which was functionally expressed in Escherichia coli. Orf 4 was also truncated by molecular cloning and encodes 99 aa of the N-t erminal moiety of a protein that displays significant homology (40% f identity) with the antiterminator LicT of B. subtilis. Transcriptional analysis revealed that the sodA gene of S. agalactiae NEM318 was tran scribed monocistronically from a promoter, the activity of which is ne ither regulated by pH, O-2, nor CO2 concentrations of the culture medi um. Analysis by high resolution agarose gel electrophoresis of the Alu I DNA polymorphism of the sodA locus in wild-type strains of S. agalac tiae belonging to serogroups I, II, or III revealed no detectable diff erence. (C) 1997 Elsevier Science B.V.