2. Academic Validation
  3. Unusually efficient CUG initiation of an overlapping reading frame in POLG mRNA yields novel protein POLGARF

Unusually efficient CUG initiation of an overlapping reading frame in POLG mRNA yields novel protein POLGARF

  • Proc Natl Acad Sci U S A. 2020 Oct 6;117(40):24936-24946. doi: 10.1073/pnas.2001433117.
Gary Loughran 1,  Alexander V Zhdanov 1,  Maria S Mikhaylova 2,  Fedor N Rozov 3,  Petr N Datskevich 3,  Sergey I Kovalchuk 4,  Marina V Serebryakova 2,  Stephen J Kiniry 1,  Audrey M Michel 1,  Patrick B F O'Connor 1,  Dmitri B Papkovsky 1,  John F Atkins 1,  Pavel V Baranov 5 4,  Ivan N Shatsky 6,  Dmitry E Andreev 6 4
Affiliations

Affiliations

  • 1 School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland, T12 XF62.
  • 2 Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia, 119992.
  • 3 Biological Faculty, Lomonosov Moscow State University, Moscow, Russia, 119234.
  • 4 Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Moscow, Russia, 117997.
  • 5 School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland, T12 XF62; [email protected] [email protected] [email protected].
  • 6 Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia, 119992; [email protected] [email protected] [email protected].
PMID: 32958672 DOI: 10.1073/pnas.2001433117
Abstract

While near-cognate codons are frequently used for translation initiation in eukaryotes, their efficiencies are usually low (<10% compared to an AUG in optimal context). Here, we describe a rare case of highly efficient near-cognate initiation. A CUG triplet located in the 5' leader of POLG messenger RNA (mRNA) initiates almost as efficiently (∼60 to 70%) as an AUG in optimal context. This CUG directs translation of a conserved 260-triplet-long overlapping open reading frame (ORF), which we call POLGARF (POLG Alternative Reading Frame). Translation of a short upstream ORF 5' of this CUG governs the ratio between POLG (the catalytic subunit of mitochondrial DNA Polymerase) and POLGARF synthesized from a single POLG mRNA. Functional investigation of POLGARF suggests a role in extracellular signaling. While unprocessed POLGARF localizes to the nucleoli together with its interacting partner C1QBP, serum stimulation results in rapid cleavage and secretion of a POLGARF C-terminal fragment. Phylogenetic analysis shows that POLGARF evolved ∼160 million y ago due to a mammalian-wide interspersed repeat (MIR) transposition into the 5' leader sequence of the mammalian POLG gene, which became fixed in placental mammals. This discovery of POLGARF unveils a previously undescribed mechanism of de novo protein-coding gene evolution.

Keywords

5′ leader; dual coding gene; non-AUG initiation; start codon selection; uORF.

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