Abstract
PpRPOT1 and PpRPOT2 transcripts possess two in-frame AUG codons at the N-terminus. Observation of transient and stable transformants expressing the N-termini of PpRPOT fused with GFP suggested that both PpRPOT1 and PpRPOT2 are exclusively translated from the second AUG, and these are targeted to only mitochondria, although these proteins are potentially targeted to plastids when translation is forced to start from the first AUG codon. When the translation efficiency of the two AUG codons in PpRPOT1 and PpRPOT2 was evaluated using GUS reporter, the second AUG codon is used as the sole translation initiation site. One of the Arabidopsis homologs AtRpoT;2 that possesses two initiation AUG codons as do the PpRPOTs has been regarded as ′dually targeted′ protein. When the localization of AtRpoT;2 with GFP-fused constructs containing the 5′-UTR and N-terminal sequence containing two AUG codon was tested, GFP-AtRpoT;2 was localized to only mitochondria.
