Abstract
In plants, Sec-pathway is known for one of the preprotein translocation pathway into the thylakoid lumen. This pathway contains SecA, SecY and SecE proteins. In Cyanidioschyzon merolae, whose genome sequence has been completed, contains secA genes both in the cell nucleus and the plastid genome. Phylogenetic analysis of the three genes revealed that plastid-encoded SecA, SecY and SecE were closely related to those in plants while nuclear-encoded secA was related to the mycobacterial secA2 which concerns auxiliary secretion factor in bacterial Sec-pathways. Northern hybridization analysis showed that the two secAs, secY and secE were actively transcribed. The secA mutant of E. coli was not suppressed by the two secAs in C. merolae. The overexpression of plastid secA in E. coli inhibited the growth while nuclear secA did not. The results suggest that the two secAs are different in their functions.
