Lois R, Freeman L, Villeponteau B, Martinson H G
Department of Chemistry and Biochemistry, University of California, Los Angeles 90024-1569.
Mol Cell Biol. 1990 Jan;10(1):16-27. doi: 10.1128/mcb.10.1.16-27.1990.
We report active, inappropriate transcription of the chicken beta A-globin gene in normal fibroblasts, cultured MSB cells, and brain. We were unable to detect ovalbumin gene transcription in these same tissues. Most of the globin gene transcripts were found to be truncated near the beginning of the gene, suggesting the existence of a premature termination process that is preferentially active under conditions of inappropriate transcription. The inappropriately transcribed beta A-globin gene chromatin remained DNase I resistant and highly methylated. Thus, the DNase I-sensitive conformation of erythrocyte beta A chromatin was correlated not with beta A transcription per se but with beta A expression. Although both transcribed and nontranscribed genes within the globin domain exhibited the same DNase I sensitivity in erythrocyte nuclei, a housekeeping gene active in erythrocytes exhibited a different level of DNase I sensitivity. However, this gene exhibited the same level of DNase I sensitivity in both erythrocytes and a cultured cell line. These observations are consistent with the proposal (G. Blobel, Proc. Natl. Acad. Sci. USA 82:8527-8529, 1985) that the DNase I sensitivity of a gene may reflect properties of chromatin related to cotranscriptional and posttranscriptional aspects of mRNA production rather than to transcription per se.
我们报道了在正常成纤维细胞、培养的MSB细胞和大脑中鸡βA-珠蛋白基因存在活跃的、不适当的转录。在这些相同组织中，我们未能检测到卵清蛋白基因的转录。发现大多数珠蛋白基因转录本在基因起始处附近被截断，这表明存在一种提前终止过程，该过程在不适当转录条件下优先活跃。不适当转录的βA-珠蛋白基因染色质对DNase I仍具有抗性且高度甲基化。因此，红细胞βA染色质对DNase I敏感的构象与βA转录本身无关，而是与βA表达相关。尽管珠蛋白结构域内已转录和未转录的基因在红细胞核中对DNase I表现出相同的敏感性，但在红细胞中活跃的一个管家基因对DNase I的敏感性水平不同。然而，该基因在红细胞和一种培养细胞系中对DNase I的敏感性水平相同。这些观察结果与以下提议一致（G.布洛贝尔，《美国国家科学院院刊》82:8527 - 8529，1985），即基因对DNase I的敏感性可能反映了与mRNA产生的共转录和转录后方面相关的染色质特性，而不是转录本身。
