Site-Selective Monitoring of the Interaction of the SRA Domain of UHRF1 with Target DNA Sequences Labeled with 2-Aminopurine.

UHRF1 plays a central role in the maintenance and transmission of epigenetic modifications by recruiting DNMT1 to hemimethylated CpG sites via its SET and RING-associated (SRA) domain, ensuring error-free duplication of methylation profiles. To characterize SRA-induced changes in the conformation and dynamics of a target 12 bp DNA duplex as a function of the methylation status, we labeled duplexes by the environment-sensitive probe 2-aminopurine (2-Ap) at various positions near or far from the central CpG recognition site containing either a nonmodified cytosine (NM duplex), a methylated cytosine (HM duplex), or methylated cytosines on both strands (BM duplex). Steady-state and time-resolved fluorescence indicated that binding of SRA induced modest conformational and dynamical changes in NM, HM, and BM duplexes, with only slight destabilization of base pairs, restriction of global duplex flexibility, and diminution of local nucleobase mobility. Moreover, significant restriction of the local motion of residues flanking the methylcytosine in the HM duplex suggested that these residues are more rigidly bound to SRA, in line with a slightly higher affinity of the HM duplex as compared to that of the NM or BM duplex. Our results are consistent with a "reader" role, in which the SRA domain scans DNA sequences for hemimethylated CpG sites without perturbation of the structure of contacted nucleotides.