# H2BK120ub and its reader RNF169 sequentially regulate replication fork remodeling and stability

## TL;DR

This study shows that H2B ubiquitination and RNF169 help regulate replication fork stability and protect DNA during replication stress in human cells.

## Contribution

The study identifies a novel role for H2BK120ub and RNF169 in replication fork remodeling and stability in human cells.

## Key findings

- H2BK120ub accumulates at stalled replication forks in an ATR- and RAD51-dependent manner.
- RNF169 acts as a reader of H2BK120ub and limits nucleolytic degradation of nascent DNA.
- Loss of RNF20 causes defective fork reversal and unrestrained fork progression.

## Abstract

Ubiquitination of the C-terminus of histone H2B (H2BK120ub) is a key histone modification with functions in a wide array of DNA-related processes, best characterized in gene transcription and repair. A role for H2B ubiquitination in DNA replication has been postulated and investigated in yeast but is still elusive in human cells. Here, we uncovered a critical function of H2BK120ub in replication fork dynamics. H2BK120ub is present at replication forks and accumulates upon replication stress in a manner dependent on ATR and RAD51. Loss of RNF20, the main ubiquitin ligase promoting H2BK120ub, leads to RECQ1-mediated unrestrained replication fork progression and defective fork reversal upon mild replication stress, restoring fork stability in BRCA2-deficient cells. Furthermore, we identified RNF169, a factor involved in the DNA damage response and repair, as a reader of the H2BK120ub mark at stalled replication forks, where it is required to protect the nascent DNA from excessive nucleolytic degradation. Hence, RNF20, H2BK120ub and RNF169 are key novel players orchestrating replication stress response and fork plasticity in human cells.

H2B ubiquitination (H2BK120ub) is a key histone mark involved in transcription and repair, but has not been implicated in DNA replication outside of yeast. This study reveals an essential role for RNF20/40-mediated H2BK120ub in regulating replication fork dynamics in human cells.

RNF20 and H2BK120ub accumulate at stalled replication forks in an ATR- and RAD51-dependent manner.Loss of RNF20 leads to RECQ1-dependent unrestrained fork progression and impairs fork reversal.The DNA damage response factor RNF169 is a reader of H2BK120ub at stalled replication forks.RNF169 limits excessive nucleolytic degradation of nascent DNA.

RNF20 and H2BK120ub accumulate at stalled replication forks in an ATR- and RAD51-dependent manner.

Loss of RNF20 leads to RECQ1-dependent unrestrained fork progression and impairs fork reversal.

The DNA damage response factor RNF169 is a reader of H2BK120ub at stalled replication forks.

RNF169 limits excessive nucleolytic degradation of nascent DNA.

RNF20/40 accumulate at stalled replication forks to facilitate fork reversal and prevent nucleolytic degradation of nascent DNA.