Controls the transcription of genes involved in arginine and lysine metabolism. Activates transcription of several genes, including argO, lysP, lysC, asd, dapB, dapD, lysA, gdhA and argK. Acts by binding directly to their promoter or control region (PubMed:10600368, PubMed:15150242, PubMed:17504942, PubMed:21441513, PubMed:21890697). ArgP dimer by itself is able to bind the argO promoter-operator region to form a binary complex, but the formation of a ternary complex with RNA polymerase is greatly stimulated only in presence of a coeffector. Both arginine and lysine are coeffectors at the argO promoter, but only arginine is competent to activate transcription. Lysine has repressive effects (PubMed:15150242, PubMed:17504942). ArgP also mediates lysine repression of dapB, and gdhA in vivo, but via an alternative mechanism: ArgP binding is directly reduced upon the addition of lysine (PubMed:21890697). Binds in vitro to the promoter region of dnaA and to the upstream region of the nrd promoter, but these genes are probably not regulated by ArgP in vivo (PubMed:9254708, PubMed:9819053, PubMed:21890697). In vitro, binds also to the three 13-mers located in the origin region (oriC) and blocks the initiation of replication (PubMed:1733927). Specifically cleaved by the protease DegP. Cleaved ArgP can no longer interact with the oriC region in vitro. Cleavage may play an important role in the control of the protein availability. Homodimer. The amount of protein increases in the late logarithmic phase. Null mutants are more sensitive to canavanine. Belongs to the LysR transcriptional regulatory family.