Human cells express two differentially spliced forms of topoisomerase II beta mRNA

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.