The N-terminal domains of TRF1 and TRF2 regulate their ability to condense telomeric DNA

Abstract

TRF1 and TRF2 are key proteins in human telomeres, which, despite their similarities, have different behaviors upon DNA binding. Previous work has shown that unlike TRF1, TRF2 condenses telomeric, thus creating consequential negative torsion on the adjacent DNA, a property that is thought to lead to the stimulation of single-strand invasion and was proposed to favor telomeric DNA looping. In this report, we show that these activities, originating from the central TRFH domain of TRF2, are also displayed by the TRFH domain of TRF1 but are repressed in the full-length protein by the presence of an acidic domain at the N-terminus. Strikingly, a similar repression is observed on TRF2 through the binding of a TERRA-like RNA molecule to the N-terminus of TRF2. Phylogenetic and biochemical studies suggest that the N-terminal domains of TRF proteins originate from a gradual extension of the coding sequences of a duplicated ancestral gene with a consequential progressive alteration of the biochemical properties of these proteins. Overall, these data suggest that the N-termini of TRF1 and TRF2 have evolved to finely regulate their ability to condense DNA.

Functional characterization of the TERRA transcriptome at damaged telomeres

“…TRF2 and TRF1 both consist of four domains: a C-terminal MYB domain required for binding to telomeres, a flexible hinge domain involved in protein–protein interactions, a TRFH domain required for homodimerization 40 and chromatin compaction 41,42 , and a divergent amino (N)-terminal region rich in basic amino acids in TRF2 and acidic residues in TRF1. To identify the molecular properties of TRF2 involved in regulating TERRA transcription, we swapped, inspired by a previous study 41 , several domains between TRF2 and TRF1 (refs 43,44) in cDNA constructs (Fig.…”

“…Overall, these data suggest that TRF2 represses TERRA transcription through its TRFH domain. This domain may elicit this function through its capacity in structural compaction of chromatin 41,42 , making telomeres less accessible to RNAPII. Interestingly, it has recently been shown that the TRFH domain of TRF2 is also required to prevent the activation of the ATM pathway and the initial steps in the telomeric DDR 44 .…”

“…On the other hand, we observe that TRF2 directly suppresses TERRA transcription through its homodimerization domain. The TRFH domain of TRF2 has been implicated in chromatin compaction 41,42 and it might be involved in sequestering chromosome termini within the T-loop structure 48,49 , which may protect the ends of chromosomes from the DNA damage machinery. When TRF2 is removed, the higher order telomere structures are disrupted and the telomeric chromatin becomes accessible to RNAPII.…”

Nucleosome organization and chromatin dynamics in telomeres

“…Unlike TRF1, TRF2 introduces positive supercoiling, and hence negative torsion is created on the adjacent DNA (56). Interestingly, the deletion of the acidic domain in TRF1 causes it to introduce positive supercoiling into DNA (57). The TRF2-specific property is thought to lead to the stimulation of the invasion of single-stranded telomeric repeats to promote telomeric DNA looping (called a t-loop), and nucleosomes have the ability to facilitate this TRF2 activity, which may be involved in stabilizing the looped telomere structures (56,57).…”

“…Interestingly, the deletion of the acidic domain in TRF1 causes it to introduce positive supercoiling into DNA (57). The TRF2-specific property is thought to lead to the stimulation of the invasion of single-stranded telomeric repeats to promote telomeric DNA looping (called a t-loop), and nucleosomes have the ability to facilitate this TRF2 activity, which may be involved in stabilizing the looped telomere structures (56,57). Thus, we speculate that each characteristic N-terminal domain may exert unique effects on the nucleosome organization in telomeres.…”