Panozzo C, Capuano V, Fillinger S, Felenbok B
Institut de Génétique et Microbiologie, Université Paris-Sud, URA CNRS D 2225, Bâtiment 409, 91405 Orsay Cedex, France.
J Biol Chem. 1997 Sep 5;272(36):22859-65. doi: 10.1074/jbc.272.36.22859.
The alcA gene which is part of the recently identified ethanol regulon, is one of the most strongly inducible genes in Aspergillus nidulans. Its transcriptional activation is mediated by the AlcR transactivator which contains a DNA-binding domain belonging to the C6 zinc binuclear cluster family. AlcR differs from the other members of this family by several features, the most striking characteristic being its binding to both symmetric and asymmetric DNA sites with the same apparent affinity. However, AlcR is also able to bind to a single site with high affinity, suggesting that unlike the other C6 proteins, AlcR binds as a monomer. In this report, we show that AlcR targets, to be functional in vivo, have to be organized as inverted or direct repeats. In addition, we show a strong synergistic activation of alcA transcription in which the number and the position of the AlcR-binding sites are crucial. The fact that the AlcR unit for in vitro binding is a single site whereas the in vivo functional unit is a repeat opens the question of the mechanism of the strong alcA transactivation. These results show that AlcR displays both in vitro and in vivo a new range of binding specificity and provides a novel example in the C6 zinc cluster protein family.
alcA基因是最近鉴定出的乙醇调节子的一部分，是构巢曲霉中诱导性最强的基因之一。其转录激活由AlcR反式激活因子介导，AlcR含有一个属于C6锌双核簇家族的DNA结合结构域。AlcR与该家族的其他成员在几个方面存在差异，最显著的特征是它以相同的表观亲和力结合对称和不对称的DNA位点。然而，AlcR也能够以高亲和力结合单个位点，这表明与其他C6蛋白不同，AlcR以单体形式结合。在本报告中，我们表明，AlcR在体内发挥功能的靶标必须组织成反向或正向重复序列。此外，我们展示了alcA转录的强烈协同激活，其中AlcR结合位点的数量和位置至关重要。体外结合的AlcR单位是单个位点，而体内功能单位是重复序列，这一事实引发了关于alcA强烈反式激活机制的问题。这些结果表明，AlcR在体外和体内均表现出一系列新的结合特异性，并为C6锌簇蛋白家族提供了一个新的例子。
