Conserved amino acid residues in C-terminus of PERIOD 2 are involved in interaction with CRYPTOCHROME 1

We investigated the amino acid sequences of rat PERIOD2 (rPER2) that are required for interaction with CRYPTOCHROME1 (CRY1) to understand the molecular mechanism of the circadian clock. Co-immunoprecipitation assays using various C-terminal fragments of rPER2 with internal deletions revealed that amino acid residues 1179–1198 are necessary for interaction with CRY1. To identify precisely which amino acid residues are responsible for the interaction, we substituted alanine for residues conserved among PER isoforms and species. We found that more than three mutations of conserved PER2 residues impaired not only binding to CRY1 but also subsequent nuclear translocation, although mutations of non-conserved residues did not affect interaction with CRY1. Thus, the conserved amino acid residues of 1179–1198 in PER2 are apparently responsible for binding to CRY1.