Ca2+-insensitive and -sensitive E1 subunits of the 2-oxoglutarate dehydrogenase complex (OGDHC) regulate tissue-specific NADH and ATP supply by mutually exclusive OGDH exons 4a and 4b. Here we show that their splicing is enforced by distant lariat branch points (dBPs) located near the 5' splice site of the intervening intron. dBPs restrict the intron length and prevent transposon insertions, which can introduce or eliminate dBP competitors. The size restriction was imposed by a single dominant dBP in anamniotes that expanded into a conserved constellation of four dBP adenines in amniotes. The amniote clusters exhibit taxon-specific usage of individual dBPs, reflecting accessibility of their extended motifs within a stable RNA hairpin rather than U2 snRNA:dBP base-pairing. The dBP expansion took place in early terrestrial species and was followed by a uridine enrichment of large downstream polypyrimidine tracts in mammals. The dBP-protected megatracts permit reciprocal regulation of exon 4a and 4b by uridine-binding proteins, including TIA-1/TIAR and PUF60, which promote U1 and U2 snRNP recruitment to the 5' splice site and BP, respectively, but do not significantly alter the relative dBP usage. We further show that codons for residues critically contributing to protein binding sites for Ca2+ and other divalent metals confer the exon inclusion order that mirrors the Irving-Williams affinity series, linking the evolution of auxiliary splicing motifs in exons to metallome constraints. Finally, we hypothesize that the dBP-driven selection for Ca2+-dependent ATP provision by E1 facilitated evolution of endothermy by optimizing the aerobic scope in target tissues.

• MeSH
• Alternative Splicing * MeSH
• Exons MeSH
• HEK293 Cells MeSH
• Introns * MeSH
• Ketoglutarate Dehydrogenase Complex genetics   metabolism   MeSH
• Humans MeSH
• RNA, Messenger chemistry   metabolism   MeSH
• RNA Splice Sites MeSH
• Evolution, Molecular MeSH
• Vertebrates genetics   MeSH
• RNA Precursors chemistry   metabolism   MeSH
• Protein Isoforms genetics   metabolism   MeSH
• Interspersed Repetitive Sequences MeSH
• RNA Splicing Factors metabolism   MeSH
• Spliceosomes metabolism   MeSH
• Body Temperature Regulation genetics   MeSH
• Calcium metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Ketoglutarate Dehydrogenase Complex MeSH
• RNA, Messenger MeSH
• RNA Splice Sites MeSH
• RNA Precursors MeSH
• Protein Isoforms MeSH
• RNA Splicing Factors MeSH
• Calcium MeSH