THE TELOBOX, A MYB-RELATED TELOMERIC DNA-BINDING MOTIF FOUND IN PROTEINS FROM YEAST, PLANTS AND HUMAN

The yeast TTAGGG binding factor 1 (Tbf1) was identified and cloned thr ough its ability to interact with vertebrate telomeric repeats in vitr o. We show here that a sequence of 60 amino acids located in its C-ter minus is critical for DNA binding, This sequence exhibits homologies w ith Myb repeats and is conserved among five proteins from plants, two of which are known to bind telomeric-related sequences, and two protei ns from human, including the telomeric repeat binding factor (TRF) and the predicted C-terminal polypeptide, called orf2, from a yet unknown protein, We demonstrate that the 111 C-terminal residues of TRF and t he 64 orf2 residues are able to bind the human telomeric repeats speci fically, We propose to call the particular Myb-related motif found in these proteins the 'telobox'. Antibodies directed against the Tbf1 tel obox detect two proteins in nuclear and mitotic chromosome extracts fr om human cell lines, Moreover, both proteins bind specifically to telo meric repeats in vitro. TRF is likely to correspond to one of them, Ba sed on their high affinity for the telomeric repeat, we predict that T RF and orf2 play an important role at human telomeres.