Lenardo M, Pierce J W, Baltimore D
Science. 1987 Jun 19;236(4808):1573-7. doi: 10.1126/science.3109035.
Individual protein-binding sites within the mouse immunoglobulin heavy chain and kappa light chain gene enhancers were altered, making it possible to examine the functional role of the sites during transcription. The E motifs, which bind factors that are present in many if not all cells, mostly behave as transcriptional activating sites. The only known heavy chain enhancer site that binds a lymphocyte-specific factor, the "octamer" site, plays a critical role in transcription but only in a truncated form of the enhancer. In the full enhancer, no one site is crucial because of an apparent functional redundancy. The site in the kappa enhancer that binds a factor specific to mature B cells, kappa B, was crucial to the constitutive activity of the enhancer in B cells. This factor is also inducible in pre-B cells, and the site was necessary for inducibility of the kappa enhancer. Thus, the sites defined by protein binding are important for the functional activity of immunoglobulin enhancers, with the sites that bind proteins restricted in their cellular distribution playing the most important roles.
小鼠免疫球蛋白重链和κ轻链基因增强子内的各个蛋白质结合位点被改变，从而能够研究这些位点在转录过程中的功能作用。E基序可结合许多（即便不是所有）细胞中都存在的因子，大多表现为转录激活位点。唯一已知的能结合淋巴细胞特异性因子的重链增强子位点，即“八聚体”位点，在转录中起关键作用，但仅在增强子的截短形式中如此。在完整的增强子中，由于明显的功能冗余，没有一个位点是至关重要的。κ增强子中结合成熟B细胞特异性因子κB的位点，对增强子在B细胞中的组成型活性至关重要。该因子在前B细胞中也可被诱导，且该位点对于κ增强子的可诱导性是必需的。因此，由蛋白质结合所定义的位点对于免疫球蛋白增强子的功能活性很重要，其中结合细胞分布受限的蛋白质的位点发挥着最重要的作用。
