这体现了原核细胞对于通常不需要表达的一系列基因的调控策略，对于特定的在葡萄糖存在时不表达的降解一些类似乳糖、半乳糖、麦芽糖、阿拉伯糖等物质的操纵子，称之为降解物敏感型操纵子。
由启动子lacP + 操纵基因lacO + 结构基因组成。其转录受CAP正调控和lacI负调控
含有葡萄糖时，cAMP含量少——代谢阻遏
Lac操纵子基因表达受阻遏蛋白和CAP的双重调控
转录水平与启动子相关→改造启动子为强启动子 lacUV5【将启动子从TATGTT突变为TATAAT，能与大肠杆菌的σ70 结合】
The lacUV5 promoter is a mutated promoter from the Escherichia coli lac operon which is used in molecular biology to drive gene expression on a plasmid. lacUV5 is very similar to the classical lac promoter, containing just 2 base pair mutations in the -10 hexamer region, compared to the lac promoter. LacUV5 is among the most commonly used promoters in molecular biology because it requires no additional activators and it drives high levels of gene expression.
The lacUV5 promoter sequence conforms more closely to the consensus sequence recognized by bacterial sigma factors than the traditional lac promoter does. Due to this, lacUV5 recruits RNA Polymerase more effectively, thus leading to higher transcription of target genes. Additionally, unlike the lac promoter, lacUV5 works independently of activator proteins or other cis regulatory elements (apart from the -10 and -35 promoter regions). While no activators are required, lacUV5 promoter expression can be regulated by the LacI repressor and can be induced with IPTG, which is an effective inducer of protein expression when used in the concentration range of 100 μM to 1.5 mM. Due to this control, the lacUV5 promoter is commonly found on expression plasmids and is used when controllable but high levels of a product are desired.
lacUV5突变能够在没有CAP的存在下更有效地起始转录，该启动子在转录水平上只受lacI的调控，因而随后得到了更广泛采用。lacI产物是一种阻遏蛋白，能结合在操纵基因lacO 上从而阻遏转录起始。乳糖的类似物IPTG可以和lacI产物结合，使其构象改变离开lacO，从而激活转录。这种可诱导的转录调控成为了大肠杆菌表达系统载体构建的常用元件。