EXPRESSION OF THE PETE GENE ENCODING PLASTOCYANIN IN THE PHOTOSYNTHETIC PROKARYOTE, PROCHLOROTHRIX-HOLLANDICA

The expression of the petE gene encoding plastocyanin (PC) in the prok aryote Prochlorothrix hollandica is dependent on the presence of coppe r in the medium. PC protein and petE mRNA are detectable only under co pper (Cu) replete conditions, suggesting that control of PC accumulati on can occur at the level of transcription or transcript stability. Ad dition of Cu (0.3 mu M) to log-phase Cu-deficient cultures yields accu mulation of PC to detectable levels within 12 h; transfer of Cu-replet e cells to Cu-deficient medium results in a slow decrease in the level of protein likely due to dilution by cell growth. By contrast, additi on of high-affinity Cu-specific chelators to rapidly deplete Cu-grown cells of copper yields a rapid loss of PC with 2 h. These data suggest that Cu-free apoPC is turned over rapidly by proteolysis. Overall, th ese data demonstrate that regulation of PC levels as Cu levels change involve events occurring at the level of bath RNA and protein turnover . (C) 1996 Academic Press, Inc.