Abstract
Protoporphyrinogen oxidase (Protox) catalyses the oxidation of protoporphyrinogen IX to protoporphyrin IX in chlorophyll and heme synthesis. Protox is encoded by the HemY gene in eukaryotes, and by the HemG gene in Escherichia coli. Since homologues for neither HemY nor HemG were found in the genomes of most cyanobacteria, it has been suggested that these organisms have a yet-unidentified type of Protox. Interestingly, most cyanobacteria seem resistant to diphenyl-ether herbicides which are specific inhibitors of HemY-type Protox. To identify a cyanobacterial gene encoding Protox, we first introduced the Arabidopsis HemY gene into Synechocystis sp. PCC6803 and then mutagenized the cells by transposon tagging. Subsequently, we screened the tagged lines for mutants that were sensitive to diphenyl-ether herbicides. We isolated several cell lines sensitive to diphenyl-ether herbicides and identified a single gene that was tagged in these cell lines. We found that this gene was essential for Protox activity in Synechocystis.
