Structure of an HIF-1alpha -pVHL complex: hydroxyproline recognition in signaling

The ubiquitination of the hypoxia-inducible factor (HIF) by the von Hippel-Lindau tumor suppressor (pVHL) plays a central role in the cellular response to changes in oxygen availability. pVHL binds to HIF only when a conserved proline in HIF is hydroxylated, a modification that is oxygen-dependent. The 1.85 angstrom structure of a 20-residue HIF-1alpha peptide-pVHL-ElonginB-ElonginC complex shows that HIF-1alpha binds to pVHL in an extended beta strand-like conformation. The hydroxyproline inserts into a gap in the pVHL hydrophobic core, at a site that is a hotspot for tumorigenic mutations, with its 4-hydroxyl group recognized by buried serine and histidine residues. Although the beta sheet-like interactions contribute to the stability of the complex, the hydroxyproline contacts are central to the strict specificity characteristic of signaling.     

A conserved family of prolyl-4-hydroxylases that modify HIF

Mammalian cells respond to changes in oxygen availability through a conserved pathway that is regulated by the hypoxia-inducible factor (HIF). The alpha subunit of HIF is targeted for degradation under normoxic conditions by a ubiquitin-ligase complex that recognizes a hydroxylated proline residue in HIF. We identified a conserved family of HIF prolyl hydoxylase (HPH) enzymes that appear to be responsible for this posttranslational modification. In cultured mammalian cells, inappropriate accumulation of HIF caused by forced expression of the HIF-1alpha subunit under normoxic conditions was attenuated by coexpression of HPH. Suppression of HPH in cultured Drosophila melanogaster cells by RNA interference resulted in elevated expression of a hypoxia-inducible gene (LDH, encoding lactate dehydrogenase) under normoxic conditions. These findings indicate that HPH is an essential component of the pathway through which cells sense oxygen.     

水稻转录因子DREB1的克隆与原核表达

DREB类转录因子特异地与DRE顺式作用元件结合,在非生物逆境胁迫(干旱、低温、高盐)中激活胁迫诱导基因的表达,使植物能够耐受水分胁迫的影响。以顺式元件rd29A3 cis构建诱饵质粒.通过酵母单杂交方法从水稻cDNA文库中筛选获得7个阳性质粒,序列分析显示阳性质粒中插入的cDNA序列一致,根据核苷酸序列推导出cDNA编码一219个氨基酸组成的多肽,该多肽有保守的EREBP/AP2结构域,N端为核定位信号(NLS),而C端则为转录激活区域,属于EREBP/AP2类转录因子,命名为RdreB1。重新合成的RdreB1 I基因降低了GC比含量,诱导处理产生了约45 kD的特异表达的融合蛋白。     

植物NAC转录因子的研究进展

近年来,新发现的NAC转录因子是具有多种生物功能的植物特异性转录因子,其N端为150个左右保守的氨基酸组成的NAC结构域。NAC转录因子在植物生长发育、激素调节和抵抗逆境胁迫等方面发挥着重要的作用。就植物NAC转录因子的基本结构特征、生物学功能及其在植物细胞次生壁生物合成过程中的作用进行了综述。     

植物WRKY转录因子研究进展

转录因子在植物的生长发育及其对外界环境的反应中起着重要的调控作用。典型的转录因子含有DNA结合域,转录调控域,寡聚化位点和核定位信号,转录因子通过这些结构域与相应的顺式元件相互作用调控基因的表达。WRKY转录因子是植物中特有的N-端含有WRKYGQK高度保守氨基酸序列的一种转录调控因子,它能够与(T)(T)TGAC(C/T)序列(W-box)发生特异性结合,从而调节启动子中含W-box元件的调节基因和/或功能基因的表达,参与植物的各种生理生化反应。文章主要论述近年来植物WRKY转录因子的相关研究进展。