Dept. Genetics, University of Leicester,
For some time we have been performing a comparative analysis of the Thr-Gly repeat within the period (per) gene in the Diptera. Our results have suggested that this region, which shows large changes in length between species, has coevolved with its immediate flanking regions. We tested this by making a series of chimeric genes where we mixed and matched the repeat and the flanking region from different species. The results were dramatic and we were able to see mutant phenotypes ranging from complete absence of per function to temperature sensitivity of the clock. The results confirm that the repeat coevolves with its immediate flanking region, and furthermore suggest that the Thr-Gly domain, interacts with the N-terminal PAS dimerization domain. We tested this intramolecular interaction with the yeast two-hybrid system, and found a strong physical interaction between the Thr-Gly domain and PAS. The implications of this result for a model of temperature compensation for the clock are discussed.