Fig. 1: Loss of Class II PRPS associated with expanded Class I PRPS homolog repertoire.

A Phylogenetic distribution of PRPS homologs in eukaryotes, with presence/absence of NHR-containing PRPS homologs in opisthokonts. PRPSAP2 denotes orthologs of mammalian PRPSAP2; Prs1 and Prs5 represent S. cerevisiae Prs1 and Prs5, respectively. Black asterisk indicates Class II presence across most metazoans, excluding Craniata. Red asterisks indicate Class II PRPS identified in only two Nuclearia species and one Chytridomycota species. B Conserved splice site junctions among PRPS homologs across different representative organisms in Opisthokonta. Gene structures for PRPS, PRPSAP2, and Prs5-encoding genes shown with exons as colored boxes; introns not displayed. Multiple sequence alignment (MSA) of translated sequences via Clustal Omega highlights a conserved splice site junction (red arrow) with adjacent amino acids shown. Top bar shows full H. sapiens PRPS1 with RF loop (red box) and CF loop (black box). Dotted red and black lines project corresponding RF and CF loops positions, respectively onto other homologs. Insertions in RF and CF loops of PRPSAP2 and Prs5 shown with red and black hatch marks, respectively (hatch marks not to scale; NHRs vary in length). C Phylogenetic distribution of PRPS homologs in chordates. Mostly present – indicates present in most taxa. Black asterisk highlights that Class II PRPS is found in most urochordates, except Oikopleura, which has additional Class I PRPS homologs not observed in other organisms from this clade. D, E Conserved splice site junctions between PRPS1 and PRPS2 (D), and PRPSAP2 and PRPSAP1 (E) across different representative organisms in jawed Vertebrata. Gene structures for PRPS, PRPSAP2, and Prs5-encoding genes shown with exons as colored boxes; introns not displayed. Dotted red and black lines denote RF and CF loop regions, respectively; insertions in PRPSAP2 and PRPSAP1 shown as red and black hatch marks, respectively (hatch marks not to scale; NHRs vary in length).