Biological and molecular functions of two EAR motifs of Arabidopsis IAA7

Some Arabidopsis thaliana AUXIN/INDOLE ACETIC ACIDs (Aux/IAAs) were predicted to have two ETHYLENE RESPONSE FACTOR–associated Amphiphilic Repression (EAR) motifs which would be involved in repression of auxin responses by interacting with TOPLESS (TPL)/TPL-Related (TPR) corepressors. However, the function of the 2^nd EAR motif and any distinctive functions of two EAR motifs have remained to be characterized. Here, we analyzed the biological and molecular function of two EAR motifs of IAA7 by using the substitution mutant forms of the EAR motifs. The 2^nd EAR motif played a minor (compared with the 1st one) repressive role in auxin-related developmental processes such as root hair growth, primary root growth, cotyledon curling, and plant dwarfism, and also in auxinresponsive gene expression. The yeast two-hybrid assay revealed that while the 1st EAR motif played a dominant role in interacting with all TPL/TPR members, the 2^nd EAR was specifically required to interact with TPR1 and played a minor role in interaction with TPL. The protein pull-down analysis further supported the engagement of the 2^nd EAR motif in interaction with TPL and TPR1. These results indicate that two EAR motifs of IAA7 plays repressive roles in auxin responses by interacting with TPL/TPRs with specificity.     

SUMO在转录中的抑制作用

许多调控基因转录的重要蛋白质能被SUMO (small ubiquitin-related modifier)化修饰,这些蛋白质包括转录因子,转录辅助因子和染色质修饰酶.SUMO化修饰对底物蛋白的活性产生影响,在大多数情况下,与转录活性的抑制有关.最近,对SUMO化调控转录的机制有了新的认识,认为SUMO化的一个重要作用是促进转录因子与转录抑制因子之间的相互作用.另一方面,已经发现转录共抑制因子HDAC (组蛋白去乙酰化酶)可以作为SUMO化的底物、效应因子和调控因子,说明乙酰化和SUMO化之间复杂的相互作用对基因转录调控起着非常重要的作用.