A HUMAN NDP-KINASE-B SPECIFICALLY BINDS SINGLE-STRANDED POLY-PYRIMIDINE SEQUENCES

Recently, a DNA binding protein 'PUF' was purified that binds to a pol y-pyrimidine rich element in the human c-myc promoter. Cloning of the corresponding gene surprisingly identified this putative transcription factor as isoform B of the enzyme nucleoside diphosphate kinase (NDPK -B) [Postel et al, (1993) Science, 261, 478-480], the product of the p otential metastasis suppressor gene nm23-H2. Using different recombina nt NDP kinases, we demonstrate by electrophoretic mobility shift analy sis (EMSA) that the NDP kinase DNA binding properties are predominantl y observed with human isoform B. Unlike typical DNA binding proteins t hat are involved in transcriptional regulation, binding occurs to sing le-stranded DNA rather than to a double-stranded oligonucleotide. As a consequence, complexes of single-stranded DNA and NDPK-B are generate d from double-stranded oligonucleotide hybrids in an ATP independent m anner. In addition to the c-myc element, NDPK-B is binding in vitro to a variety of poly-pyrimidine rich sequences including dC or dT homo-o ligomers, (CT)n dinucleotide repeats, the initiator region of the Aden ovirus major late promoter and even poly-pyrimidine rich RNAs. The pos sible consequences of these findings in understanding the multiple rol es of NDP kinase are discussed.