CLONING, NUCLEOTIDE-SEQUENCE, AND EXPRESSION OF THE BACILLUS-SUBTILIS LON GENE

The ion gene of Escherichia coli encodes the ATP-dependent serine protease La and belongs to the family of sigma(32)-dependent heat shock genes. In this paper, we report the cloning and characterization of the ion gene from the gram-positive bacterium Bacillus subtilis. The nucleotide sequence of the ion locus, which is localized upstream of the hemAXCDBL operon, was determined. The ion gene codes for an 87-kDa protein 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 homologies among all known bacterial Lon proteins. Like the E. coli ion gene, the B. subtilis ion gene is induced by heat shock Furthermore, the amount of lon-specific mRNA is increased after salt, ethanol, and oxidative stress as well as after treatment with puromycin. The potential promoter region does not show similarities to promoters recognized by sigma(32) of E. coli but contains sequences which resemble promoters recognized by the vegetative RNA polymerase E sigma(A) of B. subtilis. A second gene designated orfX is suggested to be transcribed together with ion and encodes a protein with 195 amino acid residues and a calculated molecular weight of 22,000.