Expression inEscherichia coli:Purification and Characterization of Cyclin H, a Subunit of the Human General Transcription/DNA Repair Factor TFIIH

The human cyclin H, a protein normally associated with the cyclin-dependent kinase cdk7, was overexpressed inEscherichia coliusing a T7 RNA polymerase expression system and further purified to apparent homogeneity. The purified recombinant cyclin H is similar to the endogenous one according to the following criteria: molecular weight, microsequencing and mass spectra studies, ability to interact with cdk7, and regulatory kinase activity. The scale-up of cyclin H purification is described.