EVIDENCE FOR A HELA NUCLEAR-PROTEIN THAT BINDS SPECIFICALLY TO THE SINGLE-STRANDED D(CCCTAA)(N) TELOMERIC MOTIF

In recent years several telomere binding proteins from eukaryotic orga nisms have been identified that are able to recognise specifically the duplex telomeric DNA repeat or the G-rich 3'-ending single strand. In this paper we present experimental evidence that HeLa nuclear extract s contain a protein that binds with high specificity to the single-str anded complementary d(CCCTAA)(n) repeat. Electrophoretic mobility shif t assays show that the oligonucleotide d(CCCTAACCCTAACCCTAACCCT) forms a stable complex with this protein in the presence of up to 1000-fold excesses of single-stranded DNA and RNA competitors, but is prevented from doing so in the presence of its complementary strand. SDS-PAGE e xperiments after UV cross-linking of the complex provide an estimate o f 50 kDa for the molecular weight of this protein.