DSEF-1 is a member of the hnRNP H family of RNA-binding proteins and stimulates pre-mRNA cleavage and polyadenylation in vitro.

DSEF-1 protein selectively binds to a G-rich auxiliary sequence element which influences the efficiency of processing of the SV40 late polyadenylation signal. We have obtained cDNA clones of DSEF-1 using sequence information from tryptic peptides isolated from DSEF-1 protein purified from HeLa cells. DSEF-1 protein contains three RNA-binding motifs and is a member of the hnRNP H family of RNA-binding proteins. Recombinant DSEF-1 protein stimulated the efficiency of cleavage and polyadenylation in an AAUAAA-dependent manner in in vitro reconstitution assays. DSEF-1 protein was shown to be able to interact with several poly(A) signals that lacked a G-rich binding site using a less stringent, low ionic strength gel band shift assay. Recombinant DSEF-1 protein specifically stimulated the processing of all of the poly(A) signals tested that contained a high affinity G-rich or low affinity binding site. DSEF-1 specifically increased the level of cross-linking of the 64 kDa protein of CstF to polyadenylation substrate RNAs. These observations suggest that DSEF-1 is an auxiliary factor that assists in the assembly of the general 3'-end processing factors onto the core elements of the polyadenylation signal.