Yeast heat shock mRNAs are exported through a distinct pathway defined by Rip1p

Abstract

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.[Key Words: RNA export; heat shock; RIP1; hnRNP; RSS1/GLE1; Rev]Received July 1, 1997; revised version accepted August 28, 1997.A distinguishing feature of eukaryotic cells is the nucleus, a distinct subcellular compartment separated from the cytoplasm by the double-membraned nuclear envelope. Embedded within the nuclear envelope are nuclear pore complexes (NPCs) that serve as the only known channels for transport between the nucleus and the cytoplasm (for review, see Davis 1995;Panté and Aebi 1996). Transport of macromolecules through NPCs is signal-mediated, saturable, and energy dependent. Considerable progress has been made in recent years in identifying (1) receptor molecules that recognize nuclear localization signals (NLSs) within karyophilic proteins and mediate interactions between these proteins and NPCs, (2) a small Ras-like GTPase (Ran in metazoan cells and Gsp1p/Gsp2p in Saccharomyces cerevisiae) and its accessory proteins, which play a central role in nuclear protein import, and (3) distinct components of NPCs required for nuclear protein import (for review, see Gö rlich and

Lipopolysaccharide Induces Scavenger Receptor A Expression in Mouse Macrophages: A Divergent Response Relative to Human THP-1 Monocyte/Macrophages

“…It is known that the induction of lysozyme transcripts by LPS involves regulated sequential splicing of primary transcripts (25). This type of regulated mRNA splicing and export is known to occur in response to signaling pathways involving growth factors, nutritional status, and environmental stress (25)(26)(27)(28). However, we were unable to uncover direct evidence that LPS induced an alteration in the post-transcriptional processing of SR-A transcripts.…”

Docking of HIV-1 Vpr to the Nuclear Envelope Is Mediated by the Interaction with the Nucleoporin hCG1

“…The functional yeast homologue of hCG1, i.e. Rip1p, also localizes on both faces of the NPC, and the yeast ⌬RIP1 strain reveals a defect in the export process of the heat shock RNA (35,55). Moreover, the C-terminal domain of hCG1, showing significant identity with Rip1p, is able to restore the heat shock RNA export in the ⌬RIP1 strain, indicating that hCG1 might play a role in the export of mRNA (35).…”

The Dbp5 cycle at the nuclear pore complex during mRNA export II: nucleotide cycling and mRNP remodeling by Dbp5 are controlled by Nup159 and Gle1

“…The dbp5 RR nup42D double-mutant cells showed nuclear accumulation of poly(A) RNA (Fig. 4F), whereas the single mutants did not (Saavedra et al 1997;Stutz et al 1997). Thus, in the absence of Nup159 binding, Nup42 function is required for dbp5 RR activity in mRNA export at elevated temperatures.…”