Figure 3.

Schematic depiction of mechanisms for aaRS dual targeting. (A) A single gene can generate two transcripts by selection of alternative transcription initiation sites. One of the transcripts contains a coding region for an MTS, and leads to synthesis of mitochondria-destined protein, while the other transcript is devoid of this region hence the protein is retained in the cytosol. (B) A single pre-mRNA can generate two mature mRNAs by alternative splicing. An exon is retained in one of the transcripts and leads to synthesis of an MTS-bearing protein, which is destined to mitochondria. (C) A single mature mRNA can be translated into two proteins, through switching of the translation machinery between two start codons. (D) A single translated protein can have a weak or hidden MTS, which leads to partial retention in the cytosol.