Molecular characterization of the Bacillus stearothermophilus PV72 S-layer gene sbsB induced by oxidative stress.

S-layer protein variation from a hexagonally ordered (SbsA; 130 kDa) to a obliquely ordered (SbsB; 98 kDa) protein in Bacillus stearothermophilus PV72 is mediated by an increased oxygen supply. To elucidate the molecular basis of S-layer protein variation in B. stearothermophilus PV72, the sbsB gene, coding for the 98-kDa protein, was cloned by means of inverse PCR technology and sequenced. The sbsB coding region cloned in pUC18 was expressed in Escherichia coli, without its own regulatory upstream sequences but with its putative transcriptional terminator. The reading frame of sbsB (2,760 nucleotides) is predicted to encode a protein of 920 amino acids, including the signal sequence. Amino acid sequence comparison of SbsA and SbsB did not reveal any significant homology. The expression of sbsB in E. coli resulted in an accumulation of SbsB self-assembly products in the cytoplasm.