Sequence analysis of the sbsA gene encoding the 130-kDa surface-layer protein of Bacillus stearothermophilus strain PV72.

Bacillus stearothermophilus (Bs) contains a surface-layer (S-layer) protein (SbsA), which forms a hexagonal array on the cell wall. In order to understand the structural/functional relationship of SbsA from Bs PV72, the entire nucleotide (nt) sequence of the sbsA gene was determined from three overlapping fragments. The 3'-end was cloned and expressed in Escherichia coli, whereas the 5'-region was amplified from the genome of Bs PV72 by the polymerase chain reaction using two overlapping fragments. The open reading frame (3684 nt) of sbsA is predicted to encode a protein of 1228 amino acids (aa). The SbsA is synthesized with a leader sequence of 30 aa. The predicted SbsA aa profile was similar to most other sequenced S-layer proteins, containing more acidic than basic aa (pI 5.1) and a very low amount of sulfur-containing aa. Based on aa sequence data, SbsA has weak homology of with the S-layer proteins from B. sphaericus, Rickettsia rickettsii, B. brevis HPD31 and B. brevis 47 (OWP).