The present invention relates to a polypeptide comprising or consisting of a protein kinase domain (KD) and one or more second domain(s), said second domain(s) binding to said KD and thereby modulating the activity of said KD said polypeptide containing environmentally sensitive labels. The invention is also related to screening methods using said polypeptide, to heterocyclic inhibitors identified thereby, and the pharmaceutial use of said identified inhibitors.
