Dong Wook Lee,a,1
Jong Kyoung Kim,b,1
and Inhwan Hwanga,2
a Laboratory of Cellular Systems Biology, Division of Molecular and Life Sciences, POSTECH, Pohang 790-784, Korea
b Department of Computer Science, POSTECH, Pohang 790-784, Korea
c Laboratory of Structural Bioinformatics, Division of Molecular and Life Sciences, POSTECH, Pohang 790-784, Korea
The N-terminal transit peptides of nuclear-encoded plastid proteins are necessary and sufficient for their import into plastids, but the information encoded by these transit peptides remains elusive, as they have a high sequence diversity and lack consensus sequences or common sequence motifs. Here, we investigated the sequence information contained in transit peptides. Hierarchical clustering on transit peptides of 208 plastid proteins showed that the transit peptide sequences are grouped to multiple sequence subgroups. We selected representative proteins from seven of these multiple subgroups and confirmed that their transit peptide sequences are highly dissimilar. Protein import experiments revealed that each protein contained transit peptide-specific sequence motifs critical for protein import into chloroplasts. Bioinformatics analysis identified sequence motifs that were conserved among members of the identified subgroups. The sequence motifs identified by the two independent approaches were nearly identical or significantly overlapped. Furthermore, the accuracy of predicting a chloroplast protein was greatly increased by grouping the transit peptides into multiple sequence subgroups. Based on these data, we propose that the transit peptides are composed of multiple sequence subgroups that contain distinctive sequence motifs for chloroplast targeting.
1 These authors contributed equally to this work.
2 Address correspondence to Sanguk Kim or Inhwan Hwang.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Inhwan Hwang.