Tang, LeimingMorris, JacobWan, JiMoore, ChelseaFujita, YoshihikoGillaspie, SarahAube, EricNanda, JagpreetMarques, MaudJangal, MaikaAnderson, AbbeyCox, ChristianHiraishi, HiroyukiDong, LeimingSaito, HirohideSingh, Chingakham RanjitWitcher, MichaelTopisirovic, IvanQian, Shu-BingAsano, Katsura2018-11-132018-11-132017-11-16http://hdl.handle.net/2097/39257Citation: Tang, L., Morris, J., Wan, J., Moore, C., Fujita, Y., Gillaspie, S., … Asano, K. (2017). Competition between translation initiation factor eIF5 and its mimic protein 5MP determines non-AUG initiation rate genome-wide. Nucleic Acids Research, 45(20), 11941–11953. https://doi.org/10.1093/nar/gkx808In the human genome, translation initiation from nonAUG codons plays an important role in various gene regulation programs. However, mechanisms regulating the non-AUG initiation rate remain poorly understood. Here, we show that the non-AUG initiation rate is nearly consistent under a fixed nucleotide context in various human and insect cells. Yet, it ranges from <1% to nearly 100% compared to AUG translation, depending on surrounding sequences, including Kozak, and possibly additional nucleotide contexts. Mechanistically, this range of non-AUG initiation is controlled in part, by the eIF5-mimic protein (5MP). 5MP represses non-AUG translation by competing with eIF5 for the Met-tRNAi-binding factor eIF2. Consistently, eIF5 increases, whereas 5MP decreases translation of NAT1/EIF4G2/DAP5, whose sole start codon is GUG. By modulating eIF5 and 5MP1 expression in combination with ribosome profiling we identified a handful of previously unknown non-AUG initiation sites, some of which serve as the exclusive start codons. If the initiation rate for these codons is low, then an AUG-initiated downstream ORF prevents the generation of shorter, AUGinitiated isoforms. We propose that the homeostasis of the non-AUG translatome is maintained through balanced expression of eIF5 and 5MP.Attribution 4.0 International (CC BY 4.0)http://creativecommons.org/licenses/by/4.0/Text