Jin Chunyuan, Felsenfeld Gary
Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0540, USA.
Proc Natl Acad Sci U S A. 2006 Jan 17;103(3):574-9. doi: 10.1073/pnas.0509974103. Epub 2006 Jan 5.
We have introduced the histone variant H3.3 into chicken erythroid cell lines and examined its distribution in the neighborhood of the folate receptor (FR) and beta-globin genes by using high-resolution chromatin immunoprecipitation (ChIP). Marked incorporation of tagged H3.3 into the FR gene is confined to its upstream regulatory region and is observed whether or not the gene is transcriptionally active. Incorporation is also observed over locus control regulatory elements in the absence of transcription of genes regulated by these elements, suggesting that gene activity per se is not necessarily required to replace H3 with H3.3. Other active genes display various behaviors, either incorporating H3.3 over both the coding region and upstream regulatory region or over upstream sequences only. There is, however, no straightforward correlation between sites of H3.3 incorporation and regions of enrichment in H3 acetylation and lysine-4 methylation. In the case of FR and VEGF-D, in which incorporation is confined to upstream regions, the presence of exogenous H3 results in reduced expression, whereas H3.3 stimulates expression. This finding suggests that these histone variants can be active rather than passive participants in regulation of expression.
我们已将组蛋白变体H3.3导入鸡红细胞系，并通过高分辨率染色质免疫沉淀（ChIP）技术检测其在叶酸受体（FR）和β-珠蛋白基因附近区域的分布情况。标记的H3.3显著掺入FR基因，且仅限于其上游调控区域，无论该基因是否具有转录活性均可观察到这种掺入现象。在受这些元件调控的基因无转录的情况下，在基因座控制调控元件上也观察到了掺入现象，这表明用H3.3取代H3本身不一定需要基因活性。其他活跃基因表现出不同的行为，有的在编码区和上游调控区域均掺入H3.3，有的则仅在上游序列掺入。然而，H3.3掺入位点与H3乙酰化和赖氨酸-4甲基化富集区域之间没有直接关联。就FR和VEGF-D而言，其掺入仅限于上游区域，外源性H3的存在会导致表达降低，而H3.3则会刺激表达。这一发现表明，这些组蛋白变体在基因表达调控中可能是积极的参与者而非被动的。
