Yeast heat shock mRNAs are exported through a distinct pathway defined by Rip1p.
We reported previously that heat or ethanol shock in Saccharomyces cerevisiae leads to nuclear retention of most poly(A)+ RNA but heat shock mRNAs (encoding Hsp70 proteins Ssa1p and Ssa4p) are efficiently exported in a process that is independent of the small GTPase Ran/Gsp1p, which is essential for most nucleocytoplasmic transport. To gain further insights into proteins essential or nonessential for export of heat shock mRNAs, in situ hybridization analyses to detect mRNA and pulse-labeling of proteins were used to examine several yeast mutant strains for their ability to export heat shock mRNAs following stress. Rip1p is a 42-kD protein associated with nuclear pore complexes and contains nucleoporin-like repeat sequences. It is dispensable for growth of yeast cells under normal conditions, but we report that it is essential for the export of heat shock mRNAs following stress. When SSA4 mRNA was induced from a GAL promoter in the absence of stress, it was efficiently exported in a strain lacking RIP1, indicating that Rip1p is required for export of heat shock mRNAs only following stress. Npl3p, a key mediator of export of poly(A)+ RNA, was not required for heat shock mRNA export, whereas Rss1p/Gle1p, a NES-containing factor essential for poly(A)+ RNA export, was also required for export of heat shock mRNAs after stress. High-level expression of the HIV-1 Rev protein, but not of Rev mutants, led to a partial block in export of heat shock mRNAs following stress. The data suggest a model wherein the requirement for Npl3p defines the mRNA export pathway, the requirement for Rip1p defines a pathway used for export of heat shock mRNAs after stress, and additional factors, including Rss1p/Gle1p and several nucleoporins (Rat7p/Nup159p, Rat2p/Nup120p, and Nup145p/Rat10p), are required in both pathways.
Saavedra
C A
CA
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Hammell
C M
CM
Heath
C V
CV
Cole
C N
CN
D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins; D000431:Ethanol / Q000494:pharmacology; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D015694:Gene Products, rev / Q000096:biosynthesis; D005838:Genotype; D015497:HIV-1 / Q000235:genetics; D006360:Heat-Shock Proteins / Q000096:biosynthesis*; D006358:Hot Temperature; D008954:Models, Biological; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D014157:Transcription Factors; D054321:rev Gene Products, Human Immunodeficiency Virus
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D015694:Gene Products, rev; D006360:Heat-Shock Proteins; C077734:NPL3 protein, S cerevisiae; C109212:NUP42 protein, S cerevisiae; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D012331:RNA, Fungal; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D054321:rev Gene Products, Human Immunodeficiency Virus; D000431:Ethanol