Index >> Regulation of Protein Synthesis - Operon >> Positive Control of Protein Synthesis

The first three genes of the ara operon are ara D, ara A and ara B.

These genes specify the synthesis of an epimerase, an isomerase and a kir.ase, respectively.

An associated gene, ara C, functions as a regulator gene.

The ara C gene may act as both activator and repressor.

The regulator protein produced by the ara C gene may combine with arabinose (inducer) to form an activator protein.

This activator protein binds to the initiator site (ara I) on the operon and enhances enzyme synthesis.

In the absence of arabinose the regulator protein of ara C binds to the operator site (ara 0), and thus acts as a repressor.

Positive control may also be of the inducible or repressible type.

In the inducible system, the effector molecule is the inducer.

The inducer stimulates activator function and enables gene transcription and protein synthesis.

In the repressible system the effector molecule is the corepressor.

The corepressor prevents activator function, and thus gene transcription.