UNCL, the mammalian homologue of UNC-50, is an inner nuclear membrane RNA-binding protein

Brain Res. 2000 Sep 15;877(1):110-23. doi: 10.1016/s0006-8993(00)02692-5.

Abstract

We isolated a mammalian homologue of the C. elegans gene unc-50 that we have named UNCL. The 777 kb rat UNCL cDNA encodes a 259 amino acid protein that is expressed in a wide variety of tissues with highest mRNA levels in brain, kidney and testis. Hydropathy plot analysis and in vitro translation experiments with microsomal membranes indicate that UNCL is a transmembrane protein. Hemagglutinin tagged UNCL was stably transfected into SaOS-2 osteosarcoma cells and exhibited a nuclear rim staining pattern which was retained following extraction with 1% Triton X-100, suggesting that UNCL localizes to the inner nuclear membrane. UNCL-HA was extractable in 350 mM NaCl, suggesting that UNCL is not associated with the nuclear matrix. Homopolymer RNA-binding assays performed on in vitro translated UNCL protein and 'structural modeling by homology' suggest that UNCL binds RNA via an amino-terminal RNA Recognition-like Motif. Since unc-50 is required for expression of assembled muscle-type nicotinic receptors in the nematode we investigated whether UNCL had a similar function for mammalian nicotinic receptors. When UNCL was co-expressed with neural nicotinic receptors in Xenopus oocytes or COS cells it increased expression of functional cell surface receptors up to 1. 6-fold. We conclude that UNCL is a novel inner nuclear membrane protein that associates with RNA and is involved in the cell-surface expression of neuronal nicotinic receptors. UNCL plays a broader role because UNCL homologues are present in two yeast and a plant species, none of which express nicotinic receptors and it is also found in tissues that lack nicotinic receptors.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • DNA, Complementary / isolation & purification
  • DNA, Complementary / metabolism
  • Gene Library
  • Humans
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics
  • Membrane Proteins / isolation & purification*
  • Membrane Proteins / metabolism
  • Molecular Sequence Data
  • Nuclear Envelope / chemistry*
  • Nuclear Envelope / genetics
  • RNA, Messenger / isolation & purification
  • RNA, Messenger / metabolism
  • RNA-Binding Proteins / chemistry
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / isolation & purification*
  • RNA-Binding Proteins / metabolism
  • Rats
  • Receptors, Nicotinic / genetics
  • Receptors, Nicotinic / metabolism

Substances

  • DNA, Complementary
  • Membrane Proteins
  • RNA, Messenger
  • RNA-Binding Proteins
  • Receptors, Nicotinic
  • UNC50 protein, human
  • Unc50 protein, rat