Transcriptional elongation factor and its implication in human disease

转录延伸是RNA聚合酶II基因表达的主要调控步骤之一。延长素是一种常见的延长因子，可能与von Hippel Lindau （VHL）病相关的肿瘤发生有关。为了弄清长链蛋白生物学功能的分子基础，我们对长链蛋白A进行了基因靶向，并克隆了一个新的长链蛋白A基因家族成员——长链蛋白A3。(1)小鼠胚胎干细胞（ES）长链蛋白A基因的两个等位基因均被破坏。细胞出现明显的生长缺陷，在细胞周期的G2/M期细胞数量较多。此外，细长蛋白A缺陷细胞的DNA含量超过8n。微阵列cDNA分析和RNA保护实验均表明，在长链蛋白a缺乏的细胞中，只有至少2 ~ 3%的基因（包括细胞周期相关基因）受到影响。这些数据表明，长链蛋白A不是一般基因转录所必需的，而是细胞周期正常进行所必需的。(2)发现了一个新的长蛋白A基因家族——长蛋白A3。长链蛋白A3由553个氨基酸组成，具有SII同源性和长链蛋白BC结合序列。重组A3蛋白在转录延伸中具有活性，并结合延伸蛋白BC。生化分析表明，长链蛋白A和A3的作用可能不是互补的，而是竞争的。因此，延长蛋白A基因家族相互作用来调节另一个成员的活性。

Transcriptional elongation is one of the major regulatory steps in gene expression by RNA polymerase II. Elongin is a general elongation factor which may be involved in oncogenesis associated with von Hippel Lindau (VHL) disease. To clarify the molecular basis of biological function of elongjn, we performed gene targeting of elongin A, and also cloned a novel elongin A gene family member, elongin A3.(1) Both alleles of Elongin A gene were disrupted in mouse embryonic stem (ES) cells. The cells showed significant growth defect, and had a higher number of cells at G2/M phase of cell cycle. Furthermore, elongin A deficient cells showed DNA content over 8n. Both microarray cDNA analysis and RNA protection assay showed that only a subset of genes, at least 2〜3 %, including those of cell cycle-related genes, were affected in elongin A-deficient cells. The data suggested that elongin A is not essential for genreral gene transcription, but is required for proper progression of cell cycle.(2) A novel elongin A gene family, elongin A3, was identified. Elongin A3 was composed of 553 amino acids with SII homology and elongin BC binding sequence. Recombinant A3 protein was active in transcriptional elongation, and bind elongin BC. A biochemical assay suggested that elongin A and A3 might function in not a complementary but competitive way. Thus, elongin A gene family interacts each other to modulate activity of the another member.