Which of these is a regulatory gene? a structure of the lac operon. it contains definite structures labeled from a to e. letter a marks a gen before structural genes. letter b marks a part of the operon that consists of lac z, lac y, and lac a genes. letter c indicates a structure that moves along the operon. letter d marks lac l. this part is located before the others in the sequence. letter e indicates a molecule that can bind to structure a. which of these is a regulatory gene? a structure of the lac operon. it contains definite structures labeled from a to e. letter a marks a gen before structural genes. letter b marks a part of the operon that consists of lac z, lac y, and lac a genes. letter c indicates a structure that moves along the operon. letter d marks lac l. this part is located before the others in the sequence. letter e indicates a molecule that can bind to structure a. a b c d e