In eukaryotes, histone variants are proteins that displace their canonical counterpart in nucleosomes. Histone variant incorporation can lead to profound chromatin structure alterations thereby impacting multiple biological processes, including DNA repair, transcriptional regulation and genome stability. While the deposition of H2A.X and H2A.Z variants into chromatin has been well-defined for signaling double strand break and nucleotide excision repair and for promoting the recruitment of DNA repair machinery, roles of histone variants in base excision repair (BER) remain largely unknown. Here, we investigate the influence of histone variants from H2A family on global excision of uracil initiated by uracil DNA glycosylase (UDG) and single-strand selective monofunctional uracil DNA glycosylase (SMUG1). Specifically, we reconstitute a population of variant-containing nucleosome core particle (NCP) substrates, which bear uracil residues at a variety of translational and rotational positions, and evaluate the global profile of UDG and SMUG1 repair in packaged DNA. We find that rotational positioning of nucleobases correlates with UDG activity in canonical NCP substrate except in the dyad region. In contrast, repair initiated by SMUG1 is significantly suppressed. Notably, some variants are observed to facilitate uracil removal in defined regions of the NCP. The results will be discussed in terms of histone protein core composition, as well as structural features and dynamics of variant-containing NCPs. Our observations reveal potential functional properties of H2A variants in BER within the context of chromatin.

Incorporating histone H2A variants facilitates global excision of uracil residues in nucleosomes

256th National Meeting (2018)

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