Transcriptional activation of the c-myc gene by the c-myb and B-myb gene products.

To identify the target genes modulated by the myb gene product (Myb), a co-transfection assay with a Myb expression plasmid was performed. Both c-Myb and B-Myb, another member of the myb gene family, trans-activated the human c-myc promoter. DNAase I footprint analysis using the bacterially expressed c-Myb, identified multiple c-Myb binding sites in the c-myc promoter region. Deletion analysis of the c-myc promoter suggested that some number of Myb binding sites, not a specific Myb binding site, is important for the c-Myb-induced trans-activation of the c-myc promoter. Using the c-myc-chloramphenicol acetyltransferase (CAT) construct as a reporter in a co-transfection assay, the domains of c-Myb required for trans-activation were examined. The functional domains of c-Myb identified using the c-myc promoter were almost the same as those identified previously with the artificial target gene containing Myb binding sites, but unlike the case with the artificial target gene the N-terminal half of the previously identified negative regulatory domains and the C-terminal 136 amino acids were required for the maximal trans-activation of the c-myc promoter. These results indicate that there are some differences in the regulation of Myb-dependent trans-activation in different target genes.     

正常人及视网膜母细胞瘤患者Rb基因启动子结构、功能和突变的研究

目的检测正常人及视网膜母细胞瘤（ＲＢ）患者Ｒｂ基因５′端调控区的ＤＮＡ序列,以及不同的ＤＮＡ片段的转录调控活性,研究Ｒｂ基因启动子的结构、功能以及突变对功能的影响和与ＲＢ发病的关系。方法应用ＳＳＣＰ分析及ＤＮＡ序列测定检测正常人及ＲＢ患者Ｒｂ基因启动子的ＤＮＡ序列和点突变;分离Ｒｂ基因５′端不同位置及不同大小的ＤＮＡ片段,通过氯霉素乙酰基转移酶做报告基因,检测不同的ＤＮＡ片段的转录调控活性。结果Ｒｂ基因产物起始密码上游３２７ｂｐ至８７ｂｐ间２４０ｂｐ的ＤＮＡ片段具有基本的启动子功能,其上游和下游的ＤＮＡ序列内可能还存在正或负转录调控元件。１００例正常人Ｒｂ基因启动子ＤＮＡ序列未见有任何变异,但３０２例ＲＢ患者中５例有点突变并伴有ＣＡＴ活性明显降低。结论Ｒｂ基因启动子的ＤＮＡ序列非常稳定,其突变常常导致启动子活性下降,并与视网膜母细胞瘤的遗传易感性有关