Adachi N, Kobayashi M, Koyama H
Kihara Institute for Biological Research, Yokohama City University, Totsuka-ku, Japan.
Biochem Biophys Res Commun. 1997 Jan 3;230(1):105-9. doi: 10.1006/bbrc.1996.5893.
Expression of DNA topoisomerase (topo) IIalpha varies through the cell cycle with its peak in G2/M. To investigate the mechanism controlling the topo IIalpha gene expression, we cloned the 5' upstream region of the mouse topo IIalpha gene. Although there was no TATA-like sequence, two GC and seven CCAAT boxes were found in the upstream region 5' distal to the major transcription start sites, which were located 137, 124, and 105 bp upstream from the ATG start codon. Luciferase vectors with the upstream sequences were constructed and transfected into HeLa cells, followed by cell cycle arrest either in G1 by treatment with mimosine, in S with thymidine, or in G2/M with colcemid. We found that the topo IIalpha gene promoter has the cell cycle-dependent activity, which is low in G1, rises in S, and peaks in G2/M. We suggest that the level of topo IIalpha mRNA is determined by the cell cycle-regulated promoter.
DNA拓扑异构酶（topo）IIα的表达在细胞周期中变化，在G2/M期达到峰值。为了研究控制topo IIα基因表达的机制，我们克隆了小鼠topo IIα基因的5'上游区域。尽管没有类似TATA的序列，但在主要转录起始位点5'端的上游区域发现了两个GC盒和七个CCAAT盒，这些起始位点位于ATG起始密码子上游137、124和105 bp处。构建了带有上游序列的荧光素酶载体并转染到HeLa细胞中，然后通过用含羞草碱处理使细胞在G1期停滞，用胸苷使细胞在S期停滞，或用秋水仙酰胺使细胞在G2/M期停滞。我们发现topo IIα基因启动子具有细胞周期依赖性活性，在G1期较低，在S期升高，在G2/M期达到峰值。我们认为topo IIα mRNA的水平由细胞周期调节的启动子决定。
