Chung J, Sussman D J, Zeller R, Leder P
Department of Genetics, Harvard Medical School, Howard Hughes Medical Institute, Boston, Massachusetts 02115.
Cell. 1987 Dec 24;51(6):1001-8. doi: 10.1016/0092-8674(87)90586-1.
The first exon of the c-myc gene has unusual properties that suggest some further role in gene regulation. It encodes a large, evolutionarily conserved leader exon that is transcribed more frequently than the remaining exons of the c-myc gene. In what follows, we provide a possible explanation for these observations. We find that the major promoter of the c-myc gene is bifunctional; that is, it supports transcription by RNA polymerases II and III (pol II and III). Both enzymes initiate in vitro transcription from the major c-myc initiation site (P2), but pol III is completely blocked near the 3' end of the first exon while pol II, though partially blocked, transcribes through this region. These superimposed transcriptional activities suggest a potential regulatory mechanism by which one polymerase system could influence the activity of another.
c-myc基因的第一个外显子具有不同寻常的特性，这表明它在基因调控中可能还有其他作用。它编码一个大型的、进化上保守的前导外显子，其转录频率高于c-myc基因的其余外显子。接下来，我们对这些观察结果提供一种可能的解释。我们发现c-myc基因的主要启动子具有双功能；也就是说，它支持RNA聚合酶II和III（pol II和pol III）的转录。两种酶都从c-myc主要起始位点（P2）起始体外转录，但pol III在第一个外显子的3'端附近完全受阻，而pol II虽然部分受阻，但能转录通过该区域。这些叠加的转录活性提示了一种潜在的调控机制，即一个聚合酶系统可能影响另一个聚合酶系统的活性。
