Transcriptional elongation factor and its implication in human disease

转录延伸是RNA聚合酶II基因表达的主要调节步骤之一。延伸蛋白是一种普遍存在的延伸因子，可能参与与von Hippel Lindau（VHL）病相关的肿瘤发生。为了阐明elongin生物学功能的分子基础，我们对elongin A进行了基因打靶，并克隆了一个新的elongin A基因家族成员elongin A3。(1)在小鼠胚胎干（ES）细胞中，Elongin A基因的两个等位基因都被破坏。细胞生长不良，G2/M期细胞数较多。此外，elongin A缺陷细胞显示DNA含量超过8 n。基因芯片分析和RNA保护试验均表明，在elongin A缺陷细胞中，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，elongin 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elongin A基因家族，elongin A3。延伸蛋白A3由553个氨基酸组成，具有SII同源性和延伸蛋白BC结合序列。重组A3蛋白具有转录延伸活性，并与延伸蛋白BC结合。生化分析表明，延伸蛋白A和A3可能不是以互补的方式而是以竞争的方式发挥作用。因此，延伸蛋白A基因家族彼此相互作用以调节另一成员的活性。

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.