Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Host cell factor is a protein that in humans is encoded by the HCFC1 gene.This gene is a member of the host cell factor family and encodes a protein with five Kelch repeats, a fibronectin-like motif, and six HCF repeats, each of which contains a highly specific cleavage signal. This nuclear coactivator is proteolytically cleaved at one of the six possible sites, resulting in the creation of an N-terminal chain and the corresponding C-terminal chain.