UPSTREAM SEQUENCE OF THE PARAHYDROXYPHENYL-PYRUVATE DIOXYGENASE (MELA) CODING REGION LEADING TO ENHANCED EXPRESSION IN SHEWANELLA-COLWELLIANA

Hyperexpression of the enzyme, parahydroxyphenylpyruvate dioxygenase ( pHPPH; melA), in the tyrosine degradative pathway yields excess homoge ntisic acid which oxidatively polymerizes to pyomelanin. Derepression of melA in Shewanella colwelliana strain D was found to result from a single base pair transition upstream of the promoter. This was the sol e lesion detected in pHPPH hyperexpressing strains. It is suggested th at a T to C transition alters the mRNA structure, exposing the ribosom e binding site, thereby enhancing translational efficiency.