Allshire R C, Javerzat J P, Redhead N J, Cranston G
Medical Research Council Human Genetics Unit, Western General Hospital, Edinburgh, Scotland.
Cell. 1994 Jan 14;76(1):157-69. doi: 10.1016/0092-8674(94)90180-5.
Chromatin structure at Schizosaccharomyces pombe centromeres is unusual. The insertion of the ura4 gene within these centromeres resulted in genetically identical cells mosaic for its expression. Placement of the ade6 gene within cen1 or cen3 resulted in red-white sectored colonies, demonstrating the instability of gene expression. The occurrence of pink colonies implied that intermediate levels of repression were established. Repression of both genes within centromeres was temperature sensitive. The chromatin structure of the ura4 gene at centromeres was altered, suggesting that the unusual chromatin encroaches into the gene and inhibits normal expression. These repressive effects at S. pombe centromeres resemble the classical phenomenon of position effect variegation imposed by Drosophila heterochromatin on nearby genes. However, since the epigenetic states can be set at intermediate levels of expression, a purely euchromatin-heterochromatin dichotomy does not apply. A model for the epigenetic regulation of genes placed within S. pombe centromeres is presented.
粟酒裂殖酵母着丝粒处的染色质结构不同寻常。ura4基因插入这些着丝粒内会导致其表达呈镶嵌性的基因相同细胞。ade6基因置于cen1或cen3内会产生红白扇形菌落，表明基因表达不稳定。粉色菌落的出现意味着建立了中等程度的抑制。着丝粒内两个基因的抑制对温度敏感。着丝粒处ura4基因的染色质结构发生改变，表明异常染色质侵入基因并抑制正常表达。粟酒裂殖酵母着丝粒处的这些抑制作用类似于果蝇异染色质对附近基因施加的经典位置效应斑驳现象。然而，由于表观遗传状态可以设定在中等表达水平，纯粹的常染色质 - 异染色质二分法并不适用。本文提出了一个关于置于粟酒裂殖酵母着丝粒内基因的表观遗传调控模型。
