DNA-BINDING PROPERTIES OF THE REPLICATION TELOMERE PROTEIN

The replication Telomere Protein, rTP, is a nuclear protein from the c iliate Euplotes crassus that appears to be a novel telomere replicatio n factor. rTP shares extensive amino acid sequence identity with the t wo proteins that bind and protect the macronuclear telomeres from the ciliates Oxytricha and Euplotes. Since the most extended regions of co nservation fail within the DNA-binding domains of the telomere-binding proteins, when rTP was first identified it was predicted to be anothe r structural telomere-binding protein, However, subsequent research de monstrated that rTP transcripts accumulate only during DNA replication and the rTP protein localizes to the sites of DNA replication within Euplotes macronuclei. We have now expressed rTP in a heterologous expr ession system and have examined the DNA-binding properties of the reco mbinant protein. We show that rTP binds specifically to the G-strand o f Euplotes telomeric DNA and hence has some of the same DNA-binding ch aracteristics as the Euplotes and Oxytricha telomere-binding proteins. However, other aspects of rTP binding are unique. in particular, the protein exhibits a very high off-rate and can bind double-stranded DNA as well as internal tracts of telomeric sequence. We conclude that rT P and the telomere-binding proteins are members of a class of proteins that have a conserved DNA-binding motif tailored to bind the G-strand of telomeric DNA. However, the unique DNA-binding characteristics of rTP indicate that the protein has evolved to fulfil a specialized role during telomere replication.