Intrinsic hTRF1 fluorescence quenching reveals details of telomere DNA binding activity: Impact of DNA length, structure and position of telomeric repeats

The myb-DNA binding domain is characterized by a 3-alpha helical bundle and three repeats of this domain drive sequence specific DNA binding of the c-myb transcription factor. Human TRF1 contains a single myb-related domain and as a homodimer, enables the sequence specific binding of telomeric DNA. In this report we provide a kinetic assessment of hTRF1 DNA binding activity. Using intrinsic fluorescence quenching we present evidence that hTRF1 binds to both telomeric and non-telomeric DNA with kinetic discrimination to allow stable binding to telomeric tracts of DNA. The position of telomere repeats does not impact binding though the number of repeats and structure does impact binding. Kinetic analysis of DNA-dependent intrinsic tryptophan fluorescence quenching of hTRF1 revealed a two step binding process that is impacted by telomere repeat length, position, and structure. These data are consistent with existing structural and equilibrium binding data for hTRF1 recognition and binding of telomere DNA.