Which DNA segments in the lactose operon of E. coli is a trans-acting regulatory element?
Regulatory sequences in DNA are classified as cis- or trans-acting elements, depending on the mechanism of action. Cis-acting elements function only when located on the strand of DNA being regulated, relatively close to the regulated gene. The operator (0), the promoter (P), and the CAP binding site all are located just upstream from the regulated structural genes of the operon, and do not function if placed at other locations. The -galactosidase gene is one of the regulated structural genes of this operon. Trans-acting elements can function from long distances, and can even be on a different DNA molecule in the cell. The gene, which encodes the repressor protein, is an example of a trans-acting regulatory element. Because the gene encodes a diffusible product, it doesn't matter where it is placed relative to the regulated genes. Ref : Biochemistry by U. Satyanarayana 3rd edition Pgno : 567
B-galactosidase gene
Operator
Promoter
I gene
All India exam