SECA HOMOLOG IN PROTEIN-TRANSPORT WITHIN CHLOROPLASTS - EVIDENCE FOR ENDOSYMBIONT-DERIVED SORTING

The SecA protein is an essential, azide-sensitive component of the bac terial protein translocation machinery. A SecA protein homolog (CPSecA ) now identified in pea chloroplasts was purified to homogeneity. CPSe cA supported protein transport into thylakoids, the chloroplast intern al membrane network, in an azide-sensitive fashion. Only one of three pathways for protein transport into thylakoids uses the CPSecA mechani sm. The use of a bacteria-homologous mechanism in intrachloroplast pro tein transport provides evidence for conservative sorting of proteins within chloroplasts.