Davies S L, Jenkins J R, Hickson I D
Imperial Cancer Research Fund Laboratories, University of Oxford, John Radcliffe Hospital, UK.
Nucleic Acids Res. 1993 Aug 11;21(16):3719-23. doi: 10.1093/nar/21.16.3719.
Screening of a human B-cell cDNA library with a topoisomerase II beta gene-specific probe revealed the presence of two distinct forms of topoisomerase II beta cDNA. One form (designated topoisomerase II beta-1), representing the majority of the clones, would encode the topoisomerase II beta amino acid sequence reported recently [Jenkins, J.R. et al. (1992) Nucleic Acids Res., 20, 5587-5592]. The second form (designated topoisomerase II beta-2) would encode a protein containing an additional 5 amino acids inserted after Valine-23 of the topoisomerase II beta-1 protein sequence. The topoisomerase II beta-1 and beta-2 mRNAs were both widely expressed in human cell lines and tissues. Topoisomerase II beta-2 mRNA was expressed at a lower level than that of the beta-1 form, but the relative expression of the two forms varied in different cell types. Analysis of genomic DNA clones revealed that the two forms of topoisomerase II beta mRNA arose via differential splicing. These data indicate that in addition to the closely related topoisomerase II alpha and beta isozymes, there are two forms of topoisomerase II beta mRNA widely expressed in human cells.
用拓扑异构酶IIβ基因特异性探针筛选人B细胞cDNA文库，发现存在两种不同形式的拓扑异构酶IIβ cDNA。一种形式（命名为拓扑异构酶IIβ-1），代表了大多数克隆，将编码最近报道的拓扑异构酶IIβ氨基酸序列[詹金斯，J.R.等人（1992年）《核酸研究》，20，5587 - 5592]。第二种形式（命名为拓扑异构酶IIβ-2）将编码一种蛋白质，该蛋白质在拓扑异构酶IIβ-1蛋白质序列的缬氨酸-23之后插入了另外5个氨基酸。拓扑异构酶IIβ-1和β-2 mRNA在人细胞系和组织中均广泛表达。拓扑异构酶IIβ-2 mRNA的表达水平低于β-1形式，但两种形式的相对表达在不同细胞类型中有所不同。对基因组DNA克隆的分析表明，两种形式的拓扑异构酶IIβ mRNA是通过可变剪接产生的。这些数据表明，除了密切相关的拓扑异构酶IIα和β同工酶外，还有两种形式的拓扑异构酶IIβ mRNA在人细胞中广泛表达。
