Loughran, G;Zhdanov, AV;Mikhaylova, MS;Rozov, FN;Datskevich, PN;Kovalchuk, SI;Serebryakova, MV;Kiniry, SJ;Michel, AM;O'Connor, PBF;Papkovsky, DB;Atkins, JF;Baranov, PV;Shatsky, IN;Andreev, DE

2020

October

Proceedings of The National Academy of Sciences of The United States of America

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

Validated

WOS: 12 ()

START CODON SELECTION TRANSLATION INITIATION MODULATES AUTOREGULATION UPSTREAM ORFS RIBOSOME EXPRESSION CELLS REINITIATION ARCHITECTURE EXTENSIONS

117

24936

24946

While near-cognate codons are frequently used for translation ini-tiation 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 (similar to 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 similar to 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.

WASHINGTON

0027-8424

10.1073/pnas.2001433117