1. Structural genes: Three structural genes are: 

i) lac z: The z gene codes for ß - galactosidase which is primarily responsible for the hydrolysis of the disaccharide, lactose into its monomeric units galactose and glucose.

ii) lac y: The y gene codes for permease, which increases permeability of the cell to ß - galactoside. 

iii) lac a: The a gene codes for transacetylase which can transfer acetyl group to ß - galactoside.

2. Operator gene: It interacts with a protein molecule or regulator molecule, which prevents the transcription of structural genes.

3. Promoter gene: The gene possess site for RNA polymerase attachment

4. Regulator gene (i): The gene codes for a protein known as repressor protein, it is synthesized all the time from the i-gene, that’s why it is constitutive gene which is functional always.