Upstream binding transcription factor (UBTF), or upstream binding factor (UBF), is a protein that in humans is encoded by the UBTFgene.[5][6]
Gene
In humans, the UBTF gene encodes a 764 amino acid protein and is located on chromosome 17 at position q21.31.[7][8] In mice, UBTF is found on chromosome 11 [citation needed].
Structure
UBTF contains six high mobility group boxes (HMG-boxes) that allow it to bind to DNA.[9] UBTF also contains a hyperacidic carboxy-terminal domain, which is required for transcription activation, and a helix-gap-helix dimersation motif (as UBTF is thought to often act as a dimer).[9][10]
In humans, alternative splicing can give rise to either the UBTF1 or UBTF2 isoform which are 97 kD and 94 kD in mass, respectively [11] UBTF2 lacks exon 8 of the larger UBTF1 isoform which encodes a portion of HMG Box 2.[12]
Function
UBTF is a transcription factor required for expression of the 18S, 5.8S, and 28S ribosomal RNAs, along with SL1 (a complex of TBP (MIM 600075) and three TBP-associated factors or 'TAFs')[citation needed].
UBTF is a nucleolar phosphoprotein with both DNA binding and transactivation domains. Sequence-specific DNA binding to the core and upstream control elements of the human rRNA promoter is mediated through several HMG boxes.[13] [supplied by OMIM][6]
In vertebrates, UBTF plays a crucial role in maintaining rDNA chromatin in a euchromatic state. Consequently, UBTF binding is one of the characteristics of euchromatic, transcriptionally active rDNA repeats.[14]
UBTF2 has been found to regulate mRNA transcription by RNA Polymerase II.[9]
Clinical significance
UBTF may have a role in cancer. Increased UBF binding to rDNA has been observed in cancer cells and is associated with elevated rDNA transcription and tumor cell survival.[15] Supporting this, it was found that cisplatin, a chemotherapy drug, can displace UBTF from rDNA, causing a reduction in rRNA synthesis and subsequent p53-independent apoptosis.[16]
Additionally, UBTF has been found to facilitate melanoma by promoting GIT1 expression which, in turn, activates MEK1/2-ERK1/2 signaling pathways.[17]
UBTF may also be important to neurological functioning. A de novo gain-of-function mutation to UBTF (c.628G>A) has been found to cause developmental neuroregression.[12] This mutation replaces glutamic acid with lysine at position 210 of the polypeptide chain (p.Glu210Lys) which results in a stronger UBTF interaction with DNA.[18] In 2022, another likely pathogenic variant (Gln203Arg) was identified in a proband with severe early-onset developmental delay..[19]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Matera AG, Wu W, Imai H, O'Keefe CL, Chan EK (May 1997). "Molecular cloning of the RNA polymerase I transcription factor hUBF/NOR-90 (UBTF) gene and localization to 17q21.3 by fluorescence in situ hybridization and radiation hybrid mapping". Genomics. 41 (1): 135–8. doi:10.1006/geno.1997.4647. PMID9126496.
^Jones KA, Black DM, Griffiths BL, Solomon E (Dec 1995). "Localization of the Human RNA Polymerase I Transcription Factor Gene (UBTF) to the D17S183 Locus on Chromosome 17q21 and Construction of a Long-Range Restriction Map of the Region". Genomics. 30 (3): 602–4. doi:10.1006/geno.1995.1283. PMID8825649.
Whitehead CM, Winkfein RJ, Fritzler MJ, Rattner JB (1997). "ASE-1: a novel protein of the fibrillar centres of the nucleolus and nucleolus organizer region of mitotic chromosomes". Chromosoma. 106 (8): 493–502. doi:10.1007/s004120050271. PMID9426281. S2CID10684078.
Kalousek I, Krízková P (2000). "Lymphocyte mitogenic transformation is accompanied by phosphorylation of the nucleolar transcription factor UBF". Cell. Mol. Biol. (Noisy-le-grand). 46 (7): 1163–71. PMID11075946.
Seither P, Iben S, Thiry M, Grummt I (2001). "PAF67, a novel protein that is associated with the initiation-competent form of RNA polymerase I". Biol. Chem. 382 (8): 1163–70. doi:10.1515/BC.2001.146. PMID11592397. S2CID28819190.
Dühr S, Torres-Montaner A, Astola A, García-Cozar FJ, Pendón C, Bolívar J, Valdivia MM (2001). "Molecular analysis of the 5' region of human ribosomal transcription factor UBF". DNA Seq. 12 (4): 267–72. doi:10.3109/10425170109025001. PMID11916260. S2CID11173681.