The Tic20 gene family: phylogenetic analysis and evolutionary considerations.

Tic20 is a polytopic protein of the inner envelope membrane of chloroplasts, and it is proposed to act as a translocation channel during chloroplast protein import. By analysing 29 sequences from diverse organisms, it was evident that Tic20-related proteins form two distinct clades, termed Group 1 and Group 2. The former group includes canonical Tic20 proteins that are essential for chloroplast development, while members of the latter are of unknown function. An increased evolutionary rate, in connection with adaptation to terrestrial life, was detected in Group 1. Interestingly, the sub-cellular (genomic) localization of genes coding for Group 1 proteins differs between evolutionary lineages.