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

Abstract

The properties of human DNA helicase V (HDH V) were studied in greater detail following an improved purification procedure. From 450 g of cultured cells, <0.1 mg of pure protein was isolated. HDH V unwinds DNA unidirectionally by moving in the 3' to 5' direction along the bound strand in an ATP- and Mg(2+)-dependent fashion. The enzyme is not processive and can also unwind partial 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, suggesting that HDH V exists as a monomer in the nucleus. Microsequencing of the purified HDH V shows that this enzyme is identical to the far upstream element-binding protein (FBP), a protein that stimulates the activity of the c-myc gene by binding specifically to the 'FUSE' DNA region localized upstream of its promoter. The sequence of HDH V/FBP contains RGG motifs like HDH IV/nucleolin, HDH VIII/G3BP as well as other human RNA and DNA helicases identified by other laboratories.

The Splicing Factor FUBP1 Is Required for the Efficient Splicing of Oncogene MDM2 Pre-mRNA

“…c-MYC expression (31,32). Its direct and specific binding to RNA2 ⌬1 was confirmed by immunoblotting analyses following RNA affinity chromatography of RNA2 ⌬1 and ⌬3 in nuclear extracts of normal and damage-treated cells (Fig.…”

“…FUBP1 is single strand DNA and RNA-binding protein best known for its role as a transcriptional regulator of the proto-oncogene c-MYC in many cancer types (31,32,50,51) and also as regulator of post-transcriptional events such as translation (38) and mRNA stability (23). However, despite the fact that FUBP1 has been isolated in association with spliceosomal complexes (40) and includes four K homology domains (domains homologous to heterogeneous nuclear ribonucleoprotein K, a component of the spliceosomal H complexes (52)), its role in splicing regulation has remained speculative until recently.…”

“…However, in oligodendrogliomas, where its expression is abolished due to mutations, FUBP1 is considered a tumor suppressor (28 -30). Functionally, FUBP1 is a DNA helicase V (31) and is best known for its role in the transcriptional up-regulation of c-MYC through its binding of single-stranded DNA at the far upstream element (32) via the four tandem K homology motifs in its central domain (33,34). However, it is capable of binding singlestranded RNA and post-transcriptional functions have been described for FUBP1 in mRNA turnover and translation control (35)(36)(37)(38).…”

A homolog of FBP2/KSRP binds to localized mRNAs inXenopusoocytes

“…It is not obvious how these various activities are related or whether they need to be. However, sequencing of peptides derived from purified human DNA helicase V revealed that it is FBP; notably, this protein preparation also worked as an RNA helicase (Vindigni et al, 2001). If FBP or any of its homologs are truly RNA helicases, it may be that the protein is involved in the assembly or remodeling of RNP complexes on mRNA.…”

Far upstream element-binding protein-1, a novel caspase substrate, acts as a cross-talker between apoptosis and the c-myc oncogene

“…TFIIH is necessary for various steps during transcription open-complex formation, initiation and promoter clearance. By recruiting TFIIH, FBP may control the diverse inputs of other transcription factors into basal transcription machinery (Vindigni et al, 2001).…”