Martinez M Juanita, Sprague Karen U
Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1229, USA.
Arch Insect Biochem Physiol. 2003 Oct;54(2):55-67. doi: 10.1002/arch.10120.
To identify the protein domains responsible for its conserved and specialized functions, putative TFIIB-Related Factor (BRF) from the silkworm (Bombyx mori) was compared with BRFs from other organisms. The Bombyx BRF coding region was assembled from three separate and overlapping cDNA fragments. Fragments encoding the middle portion and the 3' end were discovered in the Bombyx mori Genome Project "Silkbase" collection through sequence homology with human BRF1, and the fragment encoding the N-terminus was isolated in our laboratory using the 5' RACE method. Southern analysis showed that silkworm BRF is encoded by a single-copy gene. Bombyx BRF contains the following domains that have been noted in all other BRFs, and that are likely, therefore, to provide highly conserved functions: a zinc finger domain, an imperfect repeat, three "BRF Homology" domains, and an acidic domain at the C-terminus. As expected from the evolutionary relationships among insects and mammals, Bombyx BRF is more similar overall to Drosophila BRF (55% identical) than to human BRF1 (42% identical). Detailed examination of individual domains reveals a remarkable exception, however. Domain II of Bombyx BRF is more similar to its human counterpart than to Drosophila Domain II. This result indicates that Domain II has undergone unusual divergence in Drosophila, and suggests a structural basis for Drosophila BRF's unique pattern of interaction with other transcription factors.
为了鉴定负责其保守和特殊功能的蛋白质结构域，将家蚕（Bombyx mori）中假定的TFIIB相关因子（BRF）与其他生物体中的BRF进行了比较。家蚕BRF编码区由三个单独且重叠的cDNA片段组装而成。通过与人BRF1的序列同源性，在家蚕基因组计划“Silkbase”文库中发现了编码中间部分和3'末端的片段，并且使用5'RACE方法在我们实验室中分离出了编码N末端的片段。Southern分析表明家蚕BRF由单拷贝基因编码。家蚕BRF包含在所有其他BRF中都已发现的以下结构域，因此可能提供高度保守的功能：一个锌指结构域、一个不完全重复序列、三个“BRF同源性”结构域以及C末端的一个酸性结构域。正如从昆虫和哺乳动物之间的进化关系所预期的那样，家蚕BRF总体上与果蝇BRF（55%相同）比与人BRF1（42%相同）更相似。然而，对各个结构域的详细检查发现了一个显著的例外。家蚕BRF的结构域II与其人类对应结构域的相似性高于与果蝇结构域II的相似性。这一结果表明结构域II在果蝇中经历了异常的分化，并为果蝇BRF与其他转录因子独特的相互作用模式提供了结构基础。
