Naora H, Xu Z Z, Miyahara K, Liszczynsky H, Seno S
Research School of Biological Sciences, Australian National University, Canberra.
Chromosome Res. 1994 May;2(3):171-83. doi: 10.1007/BF01553317.
A cis-acting interference between gene activities, which occurs when two genes lie on the same DNA strand and have an intergenic distance less than a defined length, was previously deduced when chromosomal organizations of various higher eukaryote nuclear genes in clusters were compared. In order to investigate such an interference due to arrangement of genes along chromosomes, we have isolated a few cell lines which possessed (i) human mutated c-H-ras fused with the mouse mammary tumour virus long terminal repeat and (ii) the E. coli xanthine-guanine phosphoribosyltransferase (gpt) gene with the SV40 promoter, on the same or on different DNA strands, separated by a short intergenic distance or unlinked. Since the cancerous phenotype of a cell can be readily identified due to c-H-ras expression, we examined in these cell lines whether continuous c-H-ras expression, induced by dexamethasone, is disturbed through a cis-acting gene-to-gene interaction when the expression of the neighbouring gpt gene is enforced and as a result, the cancerous state of a cell is converted to the 'normal' state. The enforced expression of the neighbouring gpt gene was shown to alter c-H-ras expression, and thus reversible conversion of a cell between cancerous and normal states occurred only when the cell possessed an optimum number of the gene pair, in which both c-H-ras and the gpt gene were on the same DNA strand. This implies that the spatial arrangement of genes in chromosomes plays an important role in the regulation of gene expression in a cluster.
当比较各种高等真核生物核基因在簇中的染色体组织时，先前推断出基因活性之间存在顺式作用干扰，这种干扰发生在两个基因位于同一条DNA链上且基因间距离小于规定长度时。为了研究由于基因沿染色体排列而产生的这种干扰，我们分离了一些细胞系，这些细胞系具有（i）与小鼠乳腺肿瘤病毒长末端重复序列融合的人突变型c-H-ras和（ii）带有SV40启动子的大肠杆菌黄嘌呤-鸟嘌呤磷酸核糖转移酶（gpt）基因，它们位于同一条或不同的DNA链上，基因间距离短或不连锁。由于细胞的癌表型可因c-H-ras表达而容易识别，我们在这些细胞系中检测了地塞米松诱导的持续c-H-ras表达，当相邻gpt基因的表达增强时，是否会通过顺式作用的基因间相互作用受到干扰，结果细胞的癌状态是否会转变为“正常”状态。结果表明，相邻gpt基因的强制表达会改变c-H-ras的表达，因此只有当细胞拥有最佳数量的基因对（其中c-H-ras和gpt基因都位于同一条DNA链上）时，细胞才能在癌状态和正常状态之间发生可逆转变。这意味着染色体中基因的空间排列在簇基因表达的调控中起重要作用。
