CLONING, NUCLEOTIDE-SEQUENCE, AND EXPRESSION OF THE BACILLUS-SUBTILISLON GENE

The ion gene of Escherichia coli encodes the ATP-dependent serine prot ease La and belongs to the family of sigma(32)-dependent heat shock ge nes. In this paper, we report the cloning and characterization of the ion gene from the gram-positive bacterium Bacillus subtilis. The nucle otide sequence of the ion locus, which is localized upstream of the he mAXCDBL operon, was determined. The ion gene codes for an 87-kDa prote in consisting of 774 amino acid residues. A comparison of the deduced amino acid sequence with previously described ion gene products from E . coli, Bacillus brevis, and Myxococcus xanthus revealed strong homolo gies among all known bacterial Lon proteins. Like the E. coli ion gene , the B. subtilis ion gene is induced by heat shock Furthermore, the a mount of lon-specific mRNA is increased after salt, ethanol, and oxida tive stress as well as after treatment with puromycin. The potential p romoter region does not show similarities to promoters recognized by s igma(32) of E. coli but contains sequences which resemble promoters re cognized by the vegetative RNA polymerase E sigma(A) of B. subtilis. A second gene designated orfX is suggested to be transcribed together w ith ion and encodes a protein with 195 amino acid residues and a calcu lated molecular weight of 22,000.