HEAT MUTAGENESIS IN BACTERIOPHAGE-T4 - ANOTHER WALK DOWN THE TRANSVERSION PATHWAY

Extracellular nonreplicating bacteriophage T4 particles accumulate mutations as functions of temperature, time, pH, and ionic environment via two mechanisms: 5-hydroxymethylcytidine deamination produces G · C → A · T transitions while a guanosine modification produces transversions. Neither frameshift mutations nor mutations at A · T base pairs are appreciably induced. We now show that heat induces G · C → T · A transversions which we suggest may arise via a G* · A mispair, in which G* is a modified guanosine that has experienced a glycosylic bond migration. The rate of this reaction at 37°C is sufficient to present a genetic hazard, particularly to large genomes; thus the lesion is probably efficiently repaired in cellular genomes.