Rose S M, Garrard W T
J Biol Chem. 1984 Jul 10;259(13):8534-44.
We have studied the nature of chromatin alterations along immunoglobulin light chain (IgL) genes during B cell development using cultured murine cell lines. Employing a chromatin fractionation procedure on micrococcal nuclease-treated nuclei, we demonstrate that transcriptionally active k IgL chromatin lacks a canonical nucleosomal repeat and exhibits a pronounced association with insoluble nuclear material but is processed by nuclease to a soluble nucleosomal component that apparently lacks histone H1 and is enriched in high mobility group proteins. Of particular significance, utilizing a variant plasmacytoma cell line that has transcriptionally inactivated one k allele via a promoter deletion, we demonstrate that transcription per se is not responsible for these novel alterations. Furthermore, we show that the chromatin encompassing germline (unrearranged) and transcriptionally silent lambda IgL alleles in k-producing plasmacytomas exhibit some of the same unusual properties that are displayed by k alleles. Finally, we demonstrate that these alterations only occur in cell lines of the lymphocyte lineage that have progressed past the early pre-B cell stage; when inactive, both k and lambda IgL genes possess typical nucleosomal packaging and co-fractionate with histone H1-containing chromatin. These findings lead us to propose a model that predicts B cell stage-specific alterations in IgL chromatin prior to gene rearrangement and transcription.
我们利用培养的小鼠细胞系研究了B细胞发育过程中免疫球蛋白轻链（IgL）基因染色质改变的性质。通过对微球菌核酸酶处理的细胞核进行染色质分级分离程序，我们证明转录活跃的κ IgL染色质缺乏典型的核小体重复序列，与不溶性核物质有明显关联，但经核酸酶处理后成为一种可溶性核小体成分，该成分显然缺乏组蛋白H1且富含高迁移率族蛋白。特别重要的是，利用一种通过启动子缺失使一个κ等位基因转录失活的变异浆细胞瘤细胞系，我们证明转录本身并非这些新改变的原因。此外，我们表明，在产生κ的浆细胞瘤中，包含种系（未重排）和转录沉默的λ IgL等位基因的染色质表现出一些与κ等位基因相同的异常特性。最后，我们证明这些改变仅发生在已越过早期前B细胞阶段的淋巴细胞系细胞系中；当处于无活性状态时，κ和λ IgL基因都具有典型的核小体包装，并与含组蛋白H1的染色质共分级分离。这些发现使我们提出一个模型，该模型预测在基因重排和转录之前IgL染色质存在B细胞阶段特异性改变。
