Differential Transcription of Bacteriophage φX174 Genes at 37°C and 42°C

To investigate how high temperature affects viral transcription, the absolute amounts of mRNA for six bacteriophage φX174 genes were compared at 37°C and 42°C using Q-PCR. At 37°C, mRNA levels for all genes were consistent with previous studies, but at 42°C mRNA levels for four genes were significantly different from levels at 37°C. Transcript levels were higher for genes B and D; the promoter before gene B appears to be up-regulated at high temperature. Levels for genes F and G were reduced at high temperature, possibly due to increased efficiency of the transcription termination signal immediately upstream of gene F. These functional changes in φX174 gene regulation at high temperature have not been described previously. Studies of phage evolution at high temperatures indicate that this difference in transcript levels is subject to adaptation.