Nuclear Export of Heat Shock and Non-Heat-Shock mRNA Occurs via Similar Pathways

Several studies of the yeast Saccharomyces cerevisiae support differential regulation of heat shock mRNA (hs mRNA) and non-hs mRNA nuclear export during stress. These include the finding that hs mRNA export at 42°C is inhibited in the absence of the nucleoporinlike protein Rip1p (also called Nup42p) (C. A. Saavedra, C. M. Hammell, C. V. Heath, and C. N. Cole, Genes Dev. 11:2845–2856, 1997; F. Stutz, J. Kantor, D. Zhang, T. McCarthy, M. Neville, and M. Rosbash, Genes Dev. 11:2857–2868, 1997). However, the results reported in this paper provide little evidence for selective non-hs mRNA retention or selective hs mRNA export under heat shock conditions. First, we do not detect a block to non-hs mRNA export at 42°C in a wild-type strain. Second, hs mRNA export appears to be mediated by the Ran system and several other factors previously reported to be important for general mRNA export. Third, the export of non-hs mRNA as well as hs mRNA is inhibited in the absence of Rip1p at 42°C. As a corollary, we find no evidence for cis-acting hs mRNA sequences that promote transport during heat shock. Taken together, our data suggest that a shift to 42°C in the absence of Rip1p impacts a late stage of transport affecting most if not all mRNA.