Activator proteins A and B are required to express gene X An

Activator proteins A and B are required to express gene X. Analysis of the DNA upstream from the gene X promoter identified an 18 bp sequence with near twofold symmetry that is required for activation. Purification of the gene A and gene B products showed that both proteins form homodimers, but neither the A nor the B homodimer binds the 18 bp site. What are the possible functions of the A and B activators with respect to the 18 bp site? Propose a test of one of your ideas.

Solution

18 bp site is an upstream activation sequence which increases the expression of neighbouring genes. The sequence may have its importance due to its consistency throughout much of the evolutionary process.

The activator proteins A and B bind to enhancer sequences and results in bringing the enhancer complex close to the promoter and thereby increases transcription.

A positive transcriptional activator in E.coli is CAP (Catabolite Activator Protein) which binds with cAMP and increases the CAP binding to a conserved DNA sequence located upstream of a target core promoter.