Interactions of Cdk7 and Kin28 with Hint/PKCI-1 and Hnt1 histidine triad proteins

Cyclin-dependent kinase 7 (Cdk7) forms a trimeric complex with cyclin H and Mat1 to form the mammalian Cdk-activating kinase, CAK, as well as a part o f the basal transcription factor TFIIH, where Cdk7 phosphorylates the C-ter minal domain (CTD) of the large subunit of RNA polymerase II. Here, we repo rt a novel interaction between Cdk7 and a histidine triad (HIT) family prot ein, Hint/PKCI-1. This interaction was initially observed in a yeast two hy brid study and subsequently verified by co-immunoprecipitation and subcellu lar localization studies, where overexpression of Cdk7 leads to partial rel ocalization of Hint to the nucleus. The physical association is independent of cyclin H binding or Cdk7 kinase activity and is conserved between the r elated Sacharomyces cerevisiae CTD kinase Kin28 and the HIT protein Hnt1. F urthermore, combination of a disruption of HNT1 and a KIN28 temperature-sen sitive allele in S. cerevisae led to highly elongated cell morphology and r educed colony formation, indicating a genetic interaction between KIN28 and HNT1. The physical and genetic interactions of Hint and Hnt1 with Cdk7 and Kin28 suggest a role for this class of histidine triad proteins in the reg ulation of Cdk7 and Kin28 functions.