The Hox Transcription Factor Ubx Ensures Somatic Myogenesis by Suppressing the Mesodermal Master Regulator Twist

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Transcription Factor Binding to Replicated DNA

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Structure of Bacterial Transcription Factor SpoIIID and Evidence for a Novel Mode of DNA Binding

SpoIIID is evolutionarily conserved in endospore-forming bacteria, and it activates or represses many genes during sporulation of Bacillus subtilis. An SpoIIID monomer binds DNA with high affinity and moderate sequence specificity. In addition to a predicted helix-turn-helix motif, SpoIIID has a C-terminal basic region that contributes to DNA binding. The nuclear magnetic resonance (NMR) solution structure of SpoIIID in complex with DNA revealed that SpoIIID does indeed have a helix-turn-helix domain and that it has a novel C-terminal helical extension. Residues in both of these regions interact with DNA, based on the NMR data and on the effects on DNA binding in vitro of SpoIIID with single-alanine substitutions. These data, as well as sequence conservation in SpoIIID binding sites, were used for information-driven docking to model the SpoIIID-DNA complex. The modeling resulted in a single cluster of models in which the recognition helix of the helix-turn-helix domain interacts with the major groove of DNA, as expected. Interestingly, the C-terminal extension, which includes two helices connected by a kink, interacts with the adjacent minor groove of DNA in the models. This predicted novel mode of binding is proposed to explain how a monomer of SpoIIID achieves high-affinity DNA binding. Since SpoIIID is conserved only in endospore-forming bacteria, which include important pathogenic Bacilli and Clostridia, whose ability to sporulate contributes to their environmental persistence, the interaction of the C-terminal extension of SpoIIID with DNA is a potential target for development of sporulation inhibitors.     

Understanding the Sequence Specificity of tRNA Binding to Elongation Factor Tu using tRNA Mutagenesis

Measuring the binding affinities of 42 single-base-pair mutants in the acceptor and TΨC stems of Saccharomyces cerevisiae tRNA^Phe to Thermus thermophilus elongation factor Tu (EF-Tu) revealed that much of the specificity for tRNA occurs at the 49-65, 50-64, and 51-63 base pairs. Introducing the same mutations at the three positions into Escherichia coli tRNA_CAG^Leu resulted in similar changes in binding affinity. Swapping the three pairs from several E. coli tRNAs into yeast tRNA^Phe resulted in chimeras with EF-Tu binding affinities similar to those for the donor tRNA. Finally, analysis of double- and triple-base-pair mutants of tRNA^Phe showed that the thermodynamic contributions at the three sites are additive, permitting reasonably accurate prediction of the EF-Tu binding affinity for all E. coli tRNAs. Thus, it appears that the thermodynamic contributions of three base pairs in the TΨC stem primarily account for tRNA binding specificity to EF-Tu.     

利用ChIP-seq技术研究转录因子EDAG在全基因组的结合谱

为揭示红系分化相关基因（erythroid differentiation associated gene, EDAG）在造血中的作用机制,利用ChIP-seq分析EDAG的全基因组结合谱.首先从产妇脐带血分离CD34+细胞,EPO诱导CD34+细胞培养5 d.利用EDAG抗体进行染色体免疫共沉淀（chromatin immunoprecipitation, ChIP）实验、Western 印迹法检测EDAG抗体的富集情况.将富集到的DNA样品进行高通量测序,最后利用生物信息学分析测序结果.成功富集染色体DNA,经高通量测序和生物信息学分析,共得到1 292个EDAG 结合位点的Peaks数目,代表了975个结合的基因且错误发现率(false discovery rate, FDR)小于00001. EDAG Peaks主要分布在基因间区和内含子区.进一步利用Q-PCR对ChIP-Seq数据进行了验证,证实EDAG可结合在检测的靶基因调控区上.将EDAG结合的基因进行基因功能（gene ontology, GO)注释,表明EDAG参与了细胞周期、细胞生长、细胞分化、细胞凋亡及信号通路等多种生物学过程.综上,利用ChIP-seq技术在促红细胞生成素（EPO）诱导分化的CD34+细胞中鉴定了1 292个EDAG结合的peaks对应975个基因,并对该结果进行了随机验证,提示EDAG广泛参与了多种生物学过程.该研究为揭示EDAG的功能及作用机制提供了线索.