The PAQosome is an eleven-subunit chaperone involved in the biogenesis of several human protein complexes. We show that ASDURF, a recently discovered upstream open reading frame (uORF) in the 5’ UTR of ASNSD1 mRNA, encodes the twelfth subunit of the PAQosome. ASDURF, displays significant structural homology to beta-prefoldins and assembles with the five known subunits of the prefoldin-like module of the PAQosome to form a heterohexameric prefoldin-like complex. A model of the PAQosome prefoldin-like module is presented. The data presented here provides an example of a eukaryotic uORF-encoded polypeptide whose function is not limited to cis-acting translational regulation of downstream coding sequence and highlights the importance of including alternative ORF products in proteomic studies.

Proteins with significant homology to human ASDURF (uniprot identifier: L0R819) were identified using the protein Basic Local Alignment Search Tool (BLASTp). A list of 116 protein sequences from different eukaryotic clades (viridiplantae, fungi, protostomia and deuterostomia) was thus compiled and merged with the unaligned full complement of 4715 proteins from the Prefoldin_2 (PF01920) Pfam entry. Alignment was performed using HMMER version 3.2.1. A phylogenetic tree was generated with FastTree version 2.1.11 which was then manually rerooted to the divergence between archaeal  and eukaryotic beta prefoldins with TreeGraph2 beta version 2.15.0-887.