Downes Brian P, Stupar Robert M, Gingerich Derek J, Vierstra Richard D
Department of Genetics, 445 Henry Mall, University of Wisconsin-Madison, Madison, WI 53706-1574, USA.
Plant J. 2003 Sep;35(6):729-42. doi: 10.1046/j.1365-313x.2003.01844.x.
Attachment of one or more ubiquitins (Ubs) to various intracellular proteins has a number of roles in plants including the selective removal of regulatory proteins by the 26S proteasome. The final step in this modification is performed by ubiquitin-protein ligases (E3s) that promote Ub transfer to appropriate targets. One important family of E3s is defined by the presence of a HECT domain, an active site first found at the C-terminus of the human E3 (E6-AP). Using a consensus HECT domain as the query, we identified a family of seven HECT-containing ubiquitin-protein ligases (UPL1-UPL7) in Arabidopsis thaliana that can be grouped into four subfamilies. The UPL3 and UPL4 subfamily encodes approximately 200-kDa proteins with four Armadillo repeats similar to those in the nuclear pore protein importin-alpha, suggesting that these E3s identify their targets through binding to nuclear localization sequences. Although T-DNA disruptions of the UPL3 locus do not affect overall growth and development of Arabidopsis, the mutants show aberrant trichome morphology. Instead of developing three branches, many upl3 trichomes contain five or more branches. The upl3 trichomes also often undergo an additional round of endoreplication resulting in enlarged nuclei with ploidy levels of up to 64C. upl3 plants are hypersensitive to gibberellic acid-3 (GA3), consistent with the role of gibberellins in trichome development. The phenotype of upl3 mutants is similar to that of kaktus, a previously described set of trichome mutants with supernumerary branches. Genetic analyses confirmed that upl3 mutants and kaktus-2 are allelic with kaktus-2 plants harboring a splice-site mutation within the UPL3-transcribed region. Collectively, the data indicate that the ubiquitination of one or more activator proteins by UPL3 is necessary to repress excess branching and endoreplication of Arabidopsis trichomes.
一个或多个泛素（Ub）与各种细胞内蛋白质的附着在植物中具有多种作用，包括通过26S蛋白酶体选择性去除调节蛋白。这种修饰的最后一步由泛素 - 蛋白连接酶（E3）执行，该酶促进Ub转移到合适的靶标上。E3的一个重要家族由存在HECT结构域定义，该活性位点最初在人E3（E6 - AP）的C末端发现。使用共有HECT结构域作为查询，我们在拟南芥中鉴定出一个包含七个含HECT结构域的泛素 - 蛋白连接酶家族（UPL1 - UPL7），可分为四个亚家族。UPL3和UPL4亚家族编码约200 kDa的蛋白质，具有四个类似于核孔蛋白输入蛋白α中的犰狳重复序列，表明这些E3通过与核定位序列结合来识别其靶标。虽然UPL3基因座的T - DNA破坏不影响拟南芥的整体生长和发育，但突变体显示出异常的毛状体形态。许多upl3毛状体不是发育出三个分支，而是包含五个或更多分支。upl3毛状体还经常经历额外一轮的核内复制，导致细胞核增大，倍性水平高达64C。upl3植物对赤霉素 - 3（GA3）高度敏感，这与赤霉素在毛状体发育中的作用一致。upl3突变体的表型与kaktus相似，kaktus是先前描述的一组具有多余分支的毛状体突变体。遗传分析证实，upl3突变体和kaktus - 2与kaktus - 2植物等位，kaktus - 2植物在UPL3转录区域内存在剪接位点突变。总体而言，数据表明UPL3对一种或多种激活蛋白的泛素化对于抑制拟南芥毛状体的过度分支和核内复制是必要的。
