ALP SUPPRESSION OF LON - DEPENDENCE ON THE SLPA GENE

We have previously found that plasmids carrying the Escherichia coli a lp gene (now to be called alpA) suppress two phenotypes of a DELTAlon protease mutant, overproduction of capsular polysaccharide and sensiti vity to UV light. Suppression of these lon phenotypes is most likely e xplained by the increased degradation of the Lon substrates responsibl e for these phenotypes. We have called this suppressing protease activ ity Alp protease. The Alp protease activity is detected in cells after introduction of plasmids carrying the alpA gene, which encodes an ope n reading frame of 70 amino acids. Insertions which abolish Alp activi ty interrupt this open reading frame. We have used Tn10 and lambdaplac Mu mutagenesis to identify a chromosomal locus, slpA, that is required for alpA+ suppression of DELTAlon. This locus maps at 57 min, close t o the chromosomal location of alpA. The expression of beta-galactosida se from a lac transcriptional fusion to slpA is increased six- to eigh tfold when the alpA+ gene is present on a multicopy plasmid. Therefore , AlpA acts as a transcriptional regulator of the slpA gene(s); activa tion of slpA transcription is necessary to suppress the phenotypes of a DELTAlon mutation. In an accompanying paper (J. E. Kirby, J. E. Trem py, and S. Gottesman, J. Bacteriol. 176:2068-2081, 1994), we show that neither AlpA nor SlpA is a component of the protease itself but that they are part of a regulatory cascade which leads to expression of the Alp protease.