Telomeric nucleosomes: mobility free from constraints

Telomeres are the specialized nucleoprotein structures that protect the ends of eukaryotic chromosomes. In higher eukaryotes, telomeres are organized in nucleosomal arrays, with an unusual shorter spacing than bulk chromatin. Electron microscopy visualizations by Nikitina and Woodcock showed that both t-loops and adjacent telomeric domains are organized in nucleosomal arrays. Moreover, telomeres are highly dynamic structures whose organization and function change throughout the cell cycle. Telomeric double stranded DNA is specifically recognized by two proteins TRF1 and TRF2. Little is known about the involvement of telomeric nucleosomes in the establishment of higher order telomere structures. Whether histones and specific telomeric proteins compete for telomeric DNA binding (and hence occupy different telomere domains) or whether nucleosomes are directly involved in the formation of the telomeric complex is a relevant issue in order to understand telomeric structure and its dynamics. To address these questions, we have studied the telomeric nucleosomal arrays organization by an in vitro system that mimic telomeric chromatin, and set up a model system to study sequence-dependent intrinsic nucleosome mobility.