# Jk Dna Gaga Motifs Are Required for Local Nucleosome Remodeling and Vk-jk Recombination

## TL;DR

This study shows that GAGA DNA motifs near Jk segments are essential for proper nucleosome positioning and efficient gene recombination in B cells.

## Contribution

The study identifies GAGA motifs as a novel requirement for nucleosome remodeling and recombination at Jk segments in B cells.

## Key findings

- GAGA motifs 5’ to Jk segments regulate local RSS accessibility and nucleosome placement.
- Restoring GAGA and RSS motifs in Jk3 restored recombination, but RSS alone did not.
- Similar GAGA motifs are found 5’ to JH 23bp-RSS, suggesting a broader role in recombination.

## Abstract

Immunoreceptor gene recombination requires complementary 12 bp and 23 bp recombination signal sequences (RSSs). In addition, at RSSs where RAG proteins assemble, recombination centers must be accessible yet have a proximate nucleosome decorated with H3K4me3 for RAG2 recruitment. In Drosophila, DNA GAGA motifs play an important role in nucleosome positioning. Herein, we report that 5’ to each functional Jk 23bp-RSS is a DNA GAGA motif conserved across mammalian species. In mice, the GAGA motif 5’ to Jk1 regulated local RSS accessibility and 5’ nucleosome placement. Furthermore, it was required for efficient Vk-Jk1 recombination. Murine Jk3 is nonfunctional, having mutations in both RSS and GAGA motifs. Adding back both GAGA and RSS motifs restored Jk3 RSS accessibility and Vk-Jk3 recombination. In contrast, the RSS alone did not significantly restore accessibility or recombination. Additionally, examination of genomic sequences revealed similar GAGA motifs 5’ to each JH 23bp-RSS. Our studies indicate that in developing B cells, specific GAGA-dependent mechanisms regulate nucleosome positioning and accessibility at Jk for efficient Vk-Jk recombination. Furthermore, our data suggest an expanded definition of recombination center-associated RSSs in B cells to include a 5’ GAGA sequence that dictates the local epigenetic state required for gene recombination.

Recombination center assembly requires a specific epigenetic topology at recombination signal sequences. Herein, we report that conserved GAGA motifs 5’ to each Jk segment are required for establishing this epigenetic topology and subsequent local gene recombination.