参考答案：

解析：operon：操纵子。是原核生物基因表达和调控的一个完整单元，其中包括结构基因、调节基因、操作子和启动子。B. Lewin在Genes中这样定义操纵子：“Operon is a complete unit of bacterial gene expression and regulation, including structural genes, regulator gene(s), and control elements in DNA recognized by regulator gene product(s).” operator：操作子。DNA分子上阻抑蛋白的结合位点，用以阻止相邻的启动子上转录的起始。B. Lewin在Genes中这样定义操作子：“Operator is the site on DNA at which a repressor protein binds to prevent transcription from initiating at the adjacent promoter.”