AN UNUSUAL ORGANIZATION OF THE GENES ENCODING CYTOCHROME B(559) IN CHLAMYDOMONAS-REINHARDTII - PSBE AND PSBF GENES ARE SEPARATELY TRANSCRIBED FROM DIFFERENT REGIONS OF THE PLASTID CHROMOSOME

The psbE and psbF genes encode the apoproteins of cytochrome b(559), a n essential component of the pigment protein complex photosystem II. T ogether with psbL and psbJ, these genes constitute a single operon in all photosynthetic organisms examined thus far. We have cloned and seq uenced the psbE and psbF genes of the Chlamydomonas reinhardtii plasti d genome. The predicted amino-terminal domains of both polypeptides ar e more basic than those of other organisms, and the sequence of the ps bE gene product indicates a departure from the 'positive-inside' rule for the insertion of proteins in the thylakoid membrane. Northern blot analysis demonstrated that psbE is transcribed into a 0.3 kb mRNA, wh ile transcription of psbF and psbL genes results in a 0.9 kb transcrip t. The splitting of the psbEFLJ operon into separate transcription uni ts suggests a unique mechanism of regulation of expression of these ge nes in C. reinhardtii.