Identification of a temperature-resistant bacteriophage phi X174 mutant.

Bacteriophage phi X174am3trD, a high temperature-resistant mutant of phi X174am3, was 10(4) times more stable than phi X174am3 as judged by its survival ratio after heat treatment at 54 degrees C for 120 min. Complementation tests showed an involvement of gene G. Sequence analysis of this gene revealed three mutation sites, one transition and two insertions. The first was a silent mutation and the others brought about a change in one amino acid and an addition of another, respectively, in the gene G protein. These changes in amino acid sequence resulted in a change in the secondary structure of the protein. A beta-turn region in part of the gene G protein of phi X174am3 was changed to an alpha-helix in phi X174am3trD. These results indicate that the temperature resistance of phi X174am3trD may be caused by elevated hydrophobicity in the mutated region or by strong interaction between the mutated gene G protein and other capsid proteins.