Copenhaver G P, Putnam C D, Denton M L, Pikaard C S
Biology Department, Washington University, St Louis, MO 63130.
Nucleic Acids Res. 1994 Jul 11;22(13):2651-7. doi: 10.1093/nar/22.13.2651.
Upstream Binding Factor (UBF) is important for activation of ribosomal RNA transcription and belongs to a family of proteins containing nucleic acid binding domains, termed HMG-boxes, with similarity to High Mobility Group (HMG) chromosomal proteins. Proteins in this family can be sequence-specific or highly sequence-tolerant binding proteins. We show that Xenopus UBF can be classified among the sequence-tolerant class. Methylation interference assays using enhancer DNA probes failed to reveal any critical nucleotides required for UBF binding. Selection by UBF of optimal binding sites among a population of enhancer oligonucleotides with randomized sequences also failed to reveal any consensus sequence. The minor groove specific drugs chromomycin A3, distamycin A and actinomycin D competed against UBF for enhancer binding, suggesting that UBF, like other HMG-box proteins, probably interacts with the minor groove. UBF also shares with other HMG box proteins the ability to bind synthetic cruciform DNA. However, UBF appears different from other HMG-box proteins in that it can bind both RNA (tRNA) and DNA. The sequence-tolerant nature of UBF-nucleic acid interactions may accommodate the rapid evolution of ribosomal RNA gene sequences.
上游结合因子（UBF）对核糖体RNA转录的激活很重要，它属于一类含有核酸结合结构域的蛋白质家族，该结构域称为HMG框，与高迁移率族（HMG）染色体蛋白相似。这个家族中的蛋白质可以是序列特异性或高度序列耐受性的结合蛋白。我们发现非洲爪蟾UBF可归类于序列耐受性类别。使用增强子DNA探针进行的甲基化干扰试验未能揭示UBF结合所需的任何关键核苷酸。UBF在具有随机序列的增强子寡核苷酸群体中选择最佳结合位点时也未能揭示任何共有序列。小沟特异性药物放线菌素A3、偏端霉素A和放线菌素D与UBF竞争增强子结合，这表明UBF与其他HMG框蛋白一样，可能与小沟相互作用。UBF还与其他HMG框蛋白一样具有结合合成十字形DNA的能力。然而，UBF似乎与其他HMG框蛋白不同，因为它既能结合RNA（tRNA）也能结合DNA。UBF与核酸相互作用的序列耐受性可能适应核糖体RNA基因序列的快速进化。
