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Phosphorylation by Sky1p promotes Npl3p shuttling and mRNA dissociation

Published online by Cambridge University Press:  07 February 2001

WENDY GILBERT ,
CHRISTIAN W. SIEBEL  and
CHRISTINE GUTHRIE
WENDY GILBERT
Affiliation:
Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143-0448, USA
CHRISTIAN W. SIEBEL
Affiliation:
Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143-0448, USA Present address: Deltagen, Inc., 1031 Bing Street, San Carlos, California 94070, USA.
CHRISTINE GUTHRIE
Affiliation:
Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143-0448, USA
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Abstract

Mammalian SR proteins are currently thought to function in mRNA export as well as splicing. They contain multiple phosphorylated serine/arginine (RS/SR) dipeptides. Although SR domains can be phosphorylated by many kinases in vitro, the physiologically relevant kinase(s), and the role(s) of these modifications in vivo have remained unclear. Npl3 is a shuttling protein in budding yeast that we showed previously to be a substrate for the mammalian SR protein kinase, SRPK1, as well as the related yeast kinase, Sky1. Here we demonstrate that Sky1p phosphorylates only one of Npl3p's eight SR/RS dipeptides. Mutation of the C-terminal RS to RA, or deletion of SKY1, results in the cytoplasmic accumulation of Npl3p. The redistribution of Npl3p is accompanied by its increased association with poly(A)+ RNA and decreased association with its import receptor, Mtr10p, in vivo. We propose that phosphorylation of Npl3p by the cytoplasmically localized Sky1p is required for efficient release of mRNA upon termination of export.

Keywords

phosphorylationRNA binding proteinRNA exportserine and arginine-rich protein kinase SRPKSR protein
Type
Research Article
Information
RNA , Volume 7 , Issue 2 , February 2001 , pp. 302 - 313
Copyright
2001 RNA Society

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