Sloan S R, Shen C P, McCarrick-Walmsley R, Kadesch T
Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
Mol Cell Biol. 1996 Dec;16(12):6900-8. doi: 10.1128/MCB.16.12.6900.
The E2A gene encodes two basic helix-loop-helix proteins designated E12 and E47. Although these proteins are widely expressed, they are required only for the B-lymphocyte lineage where DNA binding is mediated distinctively by E47 homodimers. By studying the properties of deltaE47, an N-terminal truncation of E47, we provide evidence that phosphorylation may contribute to B-cell-specific DNA binding by E47. Two serines N terminal to the deltaE47 basic helix-loop-helix domain were found to be phosphorylated in a variety of cell types but were hypophosphorylated in B cells. Phosphorylating these serines in vitro inhibited DNA binding by deltaE47 homodimers but not by deltaE47-containing heterodimers, such as deltaE47:MyoD. These results argue that hypophosphorylation may be a prerequisite for activity of E47 homodimers in B cells, suggesting the use of an inductive (nonstochastic) step in early B-cell development.
E2A基因编码两种基本的螺旋-环-螺旋蛋白，即E12和E47。尽管这些蛋白广泛表达，但它们仅在B淋巴细胞谱系中是必需的，在该谱系中，DNA结合由E47同二聚体独特地介导。通过研究E47的N端截短体deltaE47的特性，我们提供了证据表明磷酸化可能有助于E47在B细胞特异性DNA结合。在deltaE47基本螺旋-环-螺旋结构域N端的两个丝氨酸在多种细胞类型中被磷酸化，但在B细胞中磷酸化程度较低。在体外磷酸化这些丝氨酸会抑制deltaE47同二聚体的DNA结合，但不会抑制含deltaE47的异二聚体（如deltaE47:MyoD）的DNA结合。这些结果表明低磷酸化可能是E47同二聚体在B细胞中发挥活性的先决条件，这表明在早期B细胞发育中使用了诱导性（非随机）步骤。
