Structural genes of lac operon are
Jacob-Monod lac system organizes regulatory and coding modules separately into distinct genetic elements. Structural segment responsible for lactose utilization consists of three tandem genes lacZ, lacY, lacA cotranscribed as single polycistronic mRNA from promoter P downstream of operator site. Each cistron possesses independent Shine-Dalgarno site allowing separate translational initiation. Regulatory locus lacI resides upstream, expressed separately from its own promoter, producing trans-acting repressor that controls operator, not part of operon transcript itself. lacP and lacO designation combine promoter-operator, CAP site is upstream activator site, and trp genes belong to distinct repressible operon regulating tryptophan synthesis.
Ref: Alberts Fig 7-37 Lac operon structure lacZYA structural genes; NCBI Operon maps lacZ lacY lacA encode structural proteins