Botella L, Grond C, Saiga H, Edström J E
Department of Genetics, University of Lund, Sweden.
EMBO J. 1988 Dec 1;7(12):3881-8. doi: 10.1002/j.1460-2075.1988.tb03274.x.
All known Balbiani ring (BR) genes in Chironomus tentans, coding for giant secretory proteins, the sp-I family, end with a short (110 codons) 3'-end exon which is highly conserved in evolution and is structurally unrelated to the sequences characterizing the core of these proteins. We find that the expressed product, the C-terminal domain, shows sequence-specific DNA binding and that it is likely to be absent in one of the sp-I components, sp-Ib, believed to be coded by the BR2.2 gene. Immunohistochemistry shows that material with reactivity towards antibody against the C-terminal domain is present in the nuclei, and specifically enriched in Balbiani ring 1 and 2. Western blotting of extracts from isolated nuclei demonstrates a component with the same antibody reactivity and of an apparent size somewhat larger than that of the domain. The possibility is discussed that the C-terminal part, which is part of the secretion when derived from some of the BR genes, might be cleaved off and function as a feedback signal to control BR gene activity when derived from the BR2.2 gene.
摇蚊（Chironomus tentans）中所有已知的巴尔比亚尼环（BR）基因，编码巨大分泌蛋白（sp-I家族），其3'-末端外显子较短（110个密码子），在进化过程中高度保守，且在结构上与这些蛋白质核心的特征序列无关。我们发现，其表达产物即C末端结构域具有序列特异性DNA结合能力，并且在被认为由BR2.2基因编码的sp-I成分之一sp-Ib中可能不存在。免疫组织化学显示，对C末端结构域抗体有反应性的物质存在于细胞核中，并且在巴尔比亚尼环1和2中特别富集。对分离细胞核提取物的蛋白质免疫印迹分析表明，有一种成分与该抗体具有相同的反应性，其表观大小略大于该结构域。文中讨论了一种可能性，即当源自某些BR基因时作为分泌一部分的C末端部分，在源自BR2.2基因时可能会被切割下来，并作为一种反馈信号来控制BR基因的活性。
