Enhancement of frameshift mutagenesis in Salmonella typhimurium derivatives of hisC3076 by 5-azacytidine and other agents.

The yield of frameshift revertants of Salmonella typhimurium strain hisC3076 on plates containing the mutagen 9-aminoacridine (9AA) is enhanced by the addition to the selection medium of a number of chemical agents. These include 5-azacytidine (5-azaC), naladixic acid, ethyl methanesulphonate; pre-treatment of cells with u.v. light or gamma-radiation is also effective. With the exception of u.v. which is detected as a poor mutagen in strain hisC3076, all other enhancing agents are not usually detected as mutagens in this strain. The observed synergism between 9AA and 5-azaC in recA and uvrB derivatives of hisC3076 eliminates the possibility that recA-dependent repair or excision repair is necessary. However a lack of synergism in a uvrD derivative suggests that helicase II is involved. It is suggested that the presence of 9AA in the plating medium enables the synergistic agents to be detected as mutagens.