CSTF1, also known as cleavage stimulation factor subunit 1, is one of the multiple factors required for polyadenylation of mammalian pre-mRNAs in vitro. It is functioning with cleavage-polyadenylation specificity factor, two cleavage factors, and poly(A)+ polymerase. It is involved in the 3' end processing of messenger RNA precursors. Recombinant human CSTF1, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.