Sequence-specific DNA recognition by the Myb-like domain of plant telomeric protein RTBP1

We have identified a rice gene encoding a DNA-binding protein that specific ally recognizes the telomeric repeat sequence TTTAGGG found in plants. This gene, which we refer to as RTBP1 (rice telomere-binding protein 1), encode s a polypeptide with a predicted molecular mass of 70 kDa, RTBP1 is ubiquit ously expressed in various organs and binds DNA with two or more duplex TTT AGGG repeats. The predicted protein sequence includes a single domain at th e C terminus with extensive homology to Myb-like DNA binding motif, The Myb -like domain of RTBP1 is very closely related to that of other telomere-bin ding proteins, including TRF1, TRF2, Taz1p, and Tbf1p, indicating that DNA- binding domains of telomere-binding proteins are well conserved among evolu tionarily distant species. To obtain precise information on the sequence of the DNA binding site recognized by RTBP1, we analyzed the sequence-specifi c binding properties of the isolated Myb-like domain of RTBP1. The isolated Myb-like domain was capable of sequence-specific DNA binding as a homodime r, Gel retardation analysis with a series of mutated telomere probes reveal ed that the internal GGGTTT sequence in the two-telomere repeats is critica l for binding of Myb-like domain of RTBP1, which is consistent with the mod el of the TRF1 DNA complex showing that base-specific contacts are made wit hin the sequence GGGTTA. To the best of our knowledge, RTBP1 is the first c loned gene in which the product is able to bind double-stranded telomeric D NA in plants. Because the Myb-like domain appears to be a significant motif for a large class of proteins that bind the duplex telomeric DNA, RTBP1 ma y play important roles in plant telomere function in vivo.