Fleury Delphine, Himanen Kristiina, Cnops Gerda, Nelissen Hilde, Boccardi Tommaso Matteo, Maere Steven, Beemster Gerrit T S, Neyt Pia, Anami Sylvester, Robles Pedro, Micol José Luis, Inzé Dirk, Van Lijsebettens Mieke
Department of Plant Systems Biology, Flanders Institute for Biotechnology, Ghent University, B-9052 Gent, Belgium.
Plant Cell. 2007 Feb;19(2):417-32. doi: 10.1105/tpc.106.041319. Epub 2007 Feb 28.
Chromatin modification and transcriptional activation are novel roles for E3 ubiquitin ligase proteins that have been mainly associated with ubiquitin-dependent proteolysis. We identified HISTONE MONOUBIQUITINATION1 (HUB1) (and its homolog HUB2) in Arabidopsis thaliana as RING E3 ligase proteins with a function in organ growth. We show that HUB1 is a functional homolog of the human and yeast BRE1 proteins because it monoubiquitinated histone H2B in an in vitro assay. Hub knockdown mutants had pale leaf coloration, modified leaf shape, reduced rosette biomass, and inhibited primary root growth. One of the alleles had been designated previously as ang4-1. Kinematic analysis of leaf and root growth together with flow cytometry revealed defects in cell cycle activities. The hub1-1 (ang4-1) mutation increased cell cycle duration in young leaves and caused an early entry into the endocycles. Transcript profiling of shoot apical tissues of hub1-1 (ang4-1) indicated that key regulators of the G2-to-M transition were misexpressed. Based on the mutant characterization, we postulate that HUB1 mediates gene activation and cell cycle regulation probably through chromatin modifications.
染色质修饰和转录激活是E3泛素连接酶蛋白的新功能，这些蛋白主要与泛素依赖性蛋白水解作用相关。我们在拟南芥中鉴定出组蛋白单泛素化蛋白1（HUB1）（及其同源物HUB2）是具有器官生长功能的RING E3连接酶蛋白。我们发现HUB1是人类和酵母BRE1蛋白的功能同源物，因为它在体外实验中能使组蛋白H2B单泛素化。HUB基因敲除突变体表现出叶片颜色变浅、叶形改变、莲座叶生物量减少以及主根生长受抑制。其中一个等位基因先前被命名为ang4 - 1。对叶片和根生长的运动学分析以及流式细胞术显示细胞周期活动存在缺陷。hub1 - 1（ang4 - 1）突变增加了幼叶的细胞周期持续时间，并导致过早进入内复制周期。hub1 - 1（ang4 - 1）茎尖组织的转录谱分析表明，G2到M期转换的关键调节因子表达失调。基于对突变体的表征，我们推测HUB1可能通过染色质修饰介导基因激活和细胞周期调控。
