MUTATION OF A PUTATIVE ADP-RIBOSYLATION MOTIF IN THE PASTEURELLA-MULTOCIDA TOXIN DOES NOT AFFECT MITOGENIC ACTIVITY

Pasteurella multocida toxin (PMT) is a potent mitogen for Swiss 3T3 fibroblasts and cytotoxic to embryonic bovine lung cells. Site-directed mutagenesis was used to investigate the functional significance of a three amino acid motifin PMT that is present in five other bacterial protein toxins which exhibit ADP-ribosyl transferase activity. Crude lysates of mutant clones were fully cytotoxic for embryonic bovine lung cells. Purified mutant toxin was also as effective at stimulating inositol phosphate turnover and nucleic acid synthesis as wild type toxin. We conclude that this motif has no functional significance in Pasteurella multocida toxin.