Positive regulator of the expression of the slpA gene (PubMed:7511582). When overexpressed, leads to suppression of the capsule overproduction and UV sensitivity phenotypes of cells mutant for the Lon ATP-dependent protease (PubMed:7511582). Part of the cryptic P4-like prophage CP4-57 (PubMed:7511583). Overexpression of AlpA leads to excision of the CP4-57 prophage by IntA. This inactivates ssrA (the gene upstream of the prophage) that encodes tmRNA which is required to rescue stalled ribosomes in a process known as trans-translation (PubMed:7511583).