import, protein localization, phylogenetic analysis, Tic20
Tic20 is a central, membrane-embedded component of the protein translocon of the inner envelope of chloroplasts (TIC). In Arabidopsis thaliana, four isoforms of Tic20 exist, namely atTic20-I, -II, -IV and-V. Recent studies demonstrated that the proteins are localised in the mitochondrial membrane, the chloroplast envelope membrane and in thylakoids. The protein sequences form two distinct phylogenetic subfamilies in embryophyta. Consistent with atTic20-I being the only essential isoform for chloroplast development the protein is exclusively targeted to the chloroplast’s inner envelope. In here, we discuss a possible reason for the evolutionary occurrence of the divergence of this protein family.