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Mol. Cell. Biol., Sep 1996, 5139-5146, Vol 16, No. 9
S Liang, M Hitomi, YH Hu, Y Liu and AM Tartakoff
An enormous variety of primary and secondary mRNA structures are compatible
with export from the nucleus to the cytoplasm. Therefore, there seems to be
a mechanism for RNA export which is independent of sequence recognition.
There nevertheless is likely to be some relatively uniform mechanism which
allows transcripts to be packaged as ribonucleoprotein particles, to gain
access to the periphery of the nucleus and ultimately to translocate across
nuclear pores. To study these events, we and others have generated
temperature-sensitive recessive mRNA transport (mtr) mutants of
Saccharomyces cerevisiae which accumulate poly(A)+ RNA in the nucleus at 37
degrees C. Several of the corresponding genes have been cloned. Upon
depletion of one of these proteins, Mtr4p, conspicuous amounts of nuclear
poly(A)+ RNA accumulate in association with the nucleolus. Corresponding
dense material is also seen by electron microscopy. MTR4 is essential for
growth and encodes a novel nuclear protein with a size of approximately 120
kDa. Mtr4p shares characteristic motifs with DEAD-box RNA helicases and
associates with RNA. It therefore may well affect RNA conformation. It
shows extensive homology to a human predicted gene product and the yeast
antiviral protein Ski2p. Critical residues of Mtr4p, including the mtr4-1
point mutation, have been identified. Mtr4p may serve as a chaperone which
translocates or normalizes the structure of mRNAs in preparation for
export.
Copyright © 1996, American Society for Microbiology
A DEAD-box-family protein is required for nucleocytoplasmic transport of yeast mRNA
Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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