著絲點結合蛋白：AND-1之生化及功能性分析

Abstract

先前利用蛋白質體分析篩選轉錄延伸因子FACT的交互蛋白時，發現一個鮮為人知的蛋白：AND-1。AND-1同時具有氨基端的WD40及羧基端的HMG-box區位，為一酸性核質蛋白。 現今結果指出AND-1與染色質和細胞核基質相關。AND-1特別在S phase中後期的細胞核中具有清晰的點狀分佈，此一分佈與S phase的進行有很密切的關係。進一步利用免疫染色及染色體免疫沈澱等方法，針對著絲點處結合的AND-1及其點狀分佈的構造進行研究。此外，分析其交互蛋白後證實AND-1可能與許多修剪複合體（spliceosome complex）或核糖核酸編輯酵素的關鍵因子有關。 然而， AND-1在水溶性及核基質部份的交互蛋白略顯不同，故而猜測細胞內不同區域之AND-1也許在調控或功能上各自扮演獨特的角色。利用AND-1為目標的小片段干擾核糖核酸（siRNA）進一部研究其功能上的特徵時指出，此蛋白可能與S到G2的過渡時期及染色質的組合有關。阻止AND-1的表現同時會造成細胞核的增大並增加核酸?對著絲點處α-satellite區域的活性。總和以上結果，AND-1可能為一具有多重功能的蛋白，能連結並協同轉錄、後轉錄、去氧核糖核酸複製及著絲點的形成。

In a previous proteomic-based screening for the interacting partners of the transcription elongator FACT, a novel protein, AND-1, was identified. AND-1 (acidic nucleoplasmic DNA-binding protein) is an acidic, nucleoplasmic protein that contains a WD40 domain at amino-terminus and a DNA-binding HMG-box at carboxy-terminus (Kohler et al, 1997). Current findings indicate that AND-1 is a chromatin and nuclear matrix-associated factor. Interestingly, AND-1 possesses a distinct punctate pattern of subnuclear localization especially in mid to late S-phase, which closely correlates with S phase progression in centromere. Further studies using immunostaining and chromatin immunoprecipitation methods pinpointed the centromeric association of AND-1 and its speckled structure. Additionally, interactomic analysis demonstrated that AND-1 might associate with many key factors of the spliceosome complex or RNA-editing enzymes. However, the interacting protein profiles seem slightly different between the soluble and nuclear matrix fractions, suggesting that subcellular pools of AND-1 may possess distinct regulatory or functional roles. Further functional characterization using AND-1 targeting siRNA revealed a possible link of this protein to S-G2 transition and heterochromatin assembling. Abrogation of AND-1 expression also led to enlarge nuclear size as well as increased nuclease accessibility of centromeric α-satellite region. Collectively, these observations imply that AND-1 may be a multifunctional protein that links and coordinates transcriptional and post-transcriptional events, DNA synthesis, as well as centromere organization.