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

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.