Abstract
The T4 mutations px, y and 1206 inactivate an error-prone recombination-like repair system, reducing or abolishing mutagenesis by UV irradiation, MMS, and white light irradiation in the presence of the photosensitizer 8MOP. Both px and y increase some spontaneous mutation rates and slightly enhance proflavin mutagenesis; neither mutation affects thymineless or 2AP mutagenesis appreciably, but both mildly enhance 5BU mutagenesis. The mutation hm promotes UV, MMS, photodynamic, thymineless, and base analog mutagenesis, in addition to spontaneous base pair substitution mutation. It does not, however, markedly affect proflavin mutagenesis. The px mutation maps in the vicinity of genes 41-56, and the hm mutation maps in the vicinity of genes rI-v.