Determination of the molecular mass of the transcription factor interacting with FBS2 in c-fos promoter

Eucaryotic genes are regulated by transcriptional factors binding to specific nucleotide sequences within the promoter regions of genes. These factors are present in a small copy number in the cells, and the purification and characterization of these proteins is a laborious task. To identify polypeptides interacting with FBS-2 site in nucleic extracts we used the modification of the known method of super(32)P-labeling of the polypeptides by crosslinking to radioactive DNA probes containing photoactivatable derivatives of nucleotides. The photoactivatable analogs were 5-BrdU (5-bromodeoxyuridine-5'-monophosphate) or FABdC (4N-(2-(p-azidotetrafluoro-benzamido)ethyl 1))-deoxycytidine).