SEC-INDEPENDENT PROTEIN TRANSLOCATION BY THE MAIZE HCF106 PROTEIN

The bacterial Sec and signal recognition particle (ffh-dependent) prot ein translocation mechanisms are conserved between prokaryotes and hig her plant chloroplasts. A third translocation mechanism in chloroplast s [the proton concentration difference (Delta pH) pathway] was previou sly thought to be unique. The hcf106 mutation of maize disrupts the lo calization of proteins transported through this Delta pH pathway in is olated chloroplasts. The Hcf106 gene encodes a receptor-like thylakoid membrane protein, which shows homology to open reading frames from al l completely sequenced bacterial genomes, which suggests that the Delt a pH pathway has been conserved since the endosymbiotic origin of chlo roplasts. Thus, the third protein translocation pathway, of which HCF1 06 is a component, is found in both bacteria and plants.