Identification of human DNA helicase V with the far upstream element-binding protein

The properties of human DNA helicase V (HDH V) were studied in greater deta il following an improved purification procedure. From 450 g of cultured cel ls, <0.1 mg of pure protein was isolated, HDH V unwinds DNA unidirectionall y by moving in the 3' to 5' direction along the bound strand in an ATP- and Mg2+-dependent fashion. The enzyme is not processive and can also unwind p artial RNA-RNA duplexes such as HDH IV and HDH VIII. The M-r determined by SDS-PAGE (66 kDa) corresponds to that measured under native conditions, sug gesting that HDH V exists as a monomer in the nucleus. Microsequencing of t he purified HDH V shows that this enzyme is identical to the far upstream e lement-binding protein (FBP), a protein that stimulates the activity of the c-myc gene by binding specifically to the 'FUSE' RNA region localized upst ream of its promoter. The sequence of HDH V/FBP contains RGG motifs like HD H IV/nucleolin, HDH VIII/G3BP as well as other human RNA and DNA helicases identified by other laboratories.