Crp79p, like Mex67p, is an auxiliary mRNA export factor in Schizosaccharomyces pombe

Anjan G. Thakurta¹, William A. Whalen², Jin Ho Yoon³, Anekella Bharathi⁴, Libor Kozak¹, Craig Whiteford⁵, Dona C. Love⁶, John A. Hanover⁶, and Ravi Dhar¹^*

¹ Basic Research Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
² Basic Research Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892 (present address: Department of Biology, Xavier University of Lousiana, 1 Drexel Drive, New Orleans, LA 70125)
³ Basic Research Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892 (present address: Department of Biology, Sungshin Women's University, Seoul 136-742, South Korea)
⁴ Basic Research Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892 (present address: DNA Tech. Inc., 13 Taft Ct., Rockville, MD 20850)
⁵ Advanced Technology Center, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
⁶ Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892

^* Corresponding author. E-mail address: dharr{at}mail.nih.gov.

The export of mRNA from the nucleus to the cytoplasm involves interactions of proteins with mRNA and the nuclear pore complex. We isolated Crp79p, a novel mRNA export factor from the same synthetic lethal screen that led to the identification of spMex67p in Schizosaccharomyces pombe (S.pombe). Crp79p is a 710 amino acid long protein that contains three RRM (RNA Recognition Motif) domains in tandem and a distinct C-terminus. Fused to GFP, Crp79p localizes to the cytoplasm. Similar to Mex67p, Crp79-GFP binds poly(A)⁺RNA in vivo, shuttles between the nucleus and the cytoplasm, and contains a nuclear export activity at the C-terminus that is Crm1p-independent. All of these properties are essential for Crp79p to promote mRNA export. Crp79p import into the nucleus depends on the Ran system. A domain of spMex67p previously identified as having a nuclear export activity can functionally substitute for the nuclear export activity at the C-terminus of Crp79p. Though both Crp79p and spMex67p function to export mRNA, Crp79p does not substitute for all of spMex67p functions, and is not likely a functional homologue of spMex67p. We propose that Crp79p is a non-essential mRNA export carrier in S.pombe.

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