The multi PAM2 protein Upa2 functions as novel core component of endosomal mRNA transport

EMBO Rep. 2019 Sep;20(9):e47381. doi: 10.15252/embr.201847381. Epub 2019 Jul 24.


mRNA transport determines spatiotemporal protein expression. Transport units are higher-order ribonucleoprotein complexes containing cargo mRNAs, RNA-binding proteins and accessory proteins. Endosomal mRNA transport in fungal hyphae belongs to the best-studied translocation mechanisms. Although several factors are known, additional core components are missing. Here, we describe the 232 kDa protein Upa2 containing multiple PAM2 motifs (poly[A]-binding protein [Pab1]-associated motif 2) as a novel core component. Loss of Upa2 disturbs transport of cargo mRNAs and associated Pab1. Upa2 is present on almost all transport endosomes in an mRNA-dependent manner. Surprisingly, all four PAM2 motifs are dispensable for function during unipolar hyphal growth. Instead, Upa2 harbours a novel N-terminal effector domain as important functional determinant as well as a C-terminal GWW motif for specific endosomal localisation. In essence, Upa2 meets all the criteria of a novel core component of endosomal mRNA transport and appears to carry out crucial scaffolding functions.

Keywords: MLLE domain; PAM2 motif; endosome; microtubule; poly(A)-binding protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Transport / physiology
  • Blotting, Western
  • Computational Biology
  • Endosomes / metabolism*
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism*
  • Microscopy, Fluorescence
  • Phylogeny
  • RNA, Messenger / metabolism*
  • Two-Hybrid System Techniques
  • Ustilago / genetics
  • Ustilago / metabolism*


  • Fungal Proteins
  • RNA, Messenger