Centre for Molecular Medicine and Therapeutics, BC Children's Hospital Research Institute, Department of Medical Genetics, University of British Columbia, Vancouver, Canada.
Terry Fox Laboratory, BC Cancer, Department of Medical Genetics, University of British Columbia, Vancouver, Canada.
PLoS Genet. 2021 Dec 6;17(12):e1009950. doi: 10.1371/journal.pgen.1009950. eCollection 2021 Dec.
Chromatin structure and underlying DNA accessibility is modulated by the incorporation of histone variants. H2A.Z, a variant of the H2A core histone family, plays a distinct and essential role in a diverse set of biological functions including gene regulation and maintenance of heterochromatin-euchromatin boundaries. Although it is currently unclear how the replacement of H2A with H2A.Z can regulate gene expression, the variance in their amino acid sequence likely contributes to their functional differences. To tease apart regions of H2A.Z that confer its unique identity, a set of plasmids expressing H2A-H2A.Z hybrids from the native H2A.Z promoter were examined for their ability to recapitulate H2A.Z function. First, we found that the H2A.Z M6 region was necessary and sufficient for interaction with the SWR1-C chromatin remodeler. Remarkably, the combination of only 9 amino acid changes, the H2A.Z M6 region, K79 and L81 (two amino acids in the α2-helix), were sufficient to fully rescue growth phenotypes of the htz1Δ mutant. Furthermore, combining three unique H2A.Z regions (K79 and L81, M6, C-terminal tail) was sufficient for expression of H2A.Z-dependent heterochromatin-proximal genes and GAL1 derepression. Surprisingly, hybrid constructs that restored the transcription of H2A.Z-dependent genes, did not fully recapitulate patterns of H2A.Z-specific enrichment at the tested loci. This suggested that H2A.Z function in transcription regulation may be at least partially independent of its specific localization in chromatin. Together, this work has identified three regions that can confer specific H2A.Z-identity to replicative H2A, furthering our understanding of what makes a histone variant a variant.
染色质结构和潜在的 DNA 可及性受组蛋白变体的掺入调节。H2A.Z 是组蛋白核心家族的变体，在包括基因调控和异染色质-常染色质边界维持在内的多种生物学功能中发挥独特而重要的作用。尽管目前尚不清楚用 H2A.Z 替代 H2A 如何调节基因表达，但它们的氨基酸序列差异可能有助于它们的功能差异。为了剖析赋予 H2A.Z 独特身份的区域，一组从天然 H2A.Z 启动子表达 H2A-H2A.Z 杂种的质粒被检测其是否能够重现 H2A.Z 的功能。首先，我们发现 H2A.Z M6 区域是与 SWR1-C 染色质重塑酶相互作用所必需和充分的。值得注意的是，仅 9 个氨基酸变化的组合，即 H2A.Z M6 区域、K79 和 L81（α2 螺旋中的两个氨基酸），足以完全挽救 htz1Δ 突变体的生长表型。此外，组合三个独特的 H2A.Z 区域（K79 和 L81、M6、C 末端尾巴）足以表达 H2A.Z 依赖性异染色质近端基因和 GAL1 去阻遏。令人惊讶的是，恢复 H2A.Z 依赖性基因转录的杂种构建体并没有完全重现 H2A.Z 特异性富集在测试基因座上的模式。这表明 H2A.Z 在转录调控中的功能至少部分独立于其在染色质中的特定定位。总之，这项工作确定了三个区域，它们可以赋予复制性 H2A 特定的 H2A.Z 身份，进一步了解了是什么使组蛋白变体成为变体。
