Sánchez-García I, Osada H, Forster A, Rabbitts T H
MRC Laboratory of Molecular Biology, Cambridge, UK.
EMBO J. 1993 Nov;12(11):4243-50. doi: 10.1002/j.1460-2075.1993.tb06108.x.
Recently, a new class of homeobox genes has been identified, called LIM-homeobox genes. These genes encode proteins which have two tandemly repeated cysteine motifs, referred to as LIM domains, in addition to a homeodomain. In addition, proteins with only LIM domains have been described but the function of the LIM domain is unknown. We have analysed the function of LIM domains using Isl-1 as a representative LIM-homeodomain protein. Employing protein prepared in bacterial cells, we show that the presence of the LIM domain in Isl-1 inhibits binding of the homeodomain to its DNA target. This in vitro inhibition can be released either by denaturation/renaturation of the protein or by truncation of the LIM domains. A similar inhibition is observed in vivo using reporter constructs. In addition we show that LIM domains in a chimeric protein can inhibit binding of the Ubx homeodomain to its target. The ability of LIM domains to inhibit DNA binding by the homeodomain provides a possible basis for negative regulation of LIM-homeodomain proteins in vivo.
最近，一类新的同源框基因被鉴定出来，称为LIM-同源框基因。这些基因编码的蛋白质除了含有一个同源异型域外，还有两个串联重复的半胱氨酸基序，称为LIM结构域。此外，还描述了仅含有LIM结构域的蛋白质，但LIM结构域的功能尚不清楚。我们以Isl-1作为代表性的LIM-同源异型域蛋白，分析了LIM结构域的功能。利用在细菌细胞中制备的蛋白质，我们发现Isl-1中LIM结构域的存在会抑制同源异型域与它的DNA靶点的结合。这种体外抑制作用可以通过蛋白质的变性/复性或LIM结构域的截短来解除。使用报告基因构建体在体内也观察到了类似的抑制作用。此外，我们还表明，嵌合蛋白中的LIM结构域可以抑制Ubx同源异型域与它的靶点的结合。LIM结构域抑制同源异型域与DNA结合的能力为体内LIM-同源异型域蛋白的负调控提供了一个可能的基础。
