Fig 7.

Model for the regulation of HpdR during tyrosine catabolism and CDA biosynthesis in S. coelicolor. As an autoregulator, HpdR regulates its own transcription (not shown). It also represses hppD, the product of which catalyzes the conversion of 4-hydroxyphenypyruvate (4HHP) to homogentisate, but activates hmaS, which is involved in CDA biosynthesis. During vegetative growth, l-tyrosine in the medium is catabolized to 4HHP by TyrB. The accumulated 4HHP binds to HpdR and causes it to dissociate from the hppD and hmaS promoters, therefore initiating hppD expression and preventing hmaS expression. During stationary phase, l-tyrosine in the medium is limited, 4HHP is reduced, and expression of hpdD is repressed, while hmaS expression is activated, directing 4HPP into CDA biosynthesis.