UNCL, the mammalian homologue of UNC-50, is an inner nuclear membrane RNA-binding protein.
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.
Fitzgerald
J
J
Murdoch Childrens Research Institute, and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, 3052, Parkville, Australia. fitzgerj@cryptic.rch.unimelb.edu.au
Kennedy
D
D
Viseshakul
N
N
Cohen
B N
BN
Mattick
J
J
Bateman
J F
JF
Forsayeth
J R
JR
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary / Q000302:isolation & purification / Q000378:metabolism; D015723:Gene Library; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000737:chemistry* / Q000235:genetics; D012333:RNA, Messenger / Q000302:isolation & purification / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D051381:Rats; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism
D018076:DNA, Complementary; D008565:Membrane Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011978:Receptors, Nicotinic; C000604212:UNC50 protein, human; C416052:Unc50 protein, rat