NUCLEOLAR ACCUMULATION OF POLY(A)(-SHOCKED YEAST-CELLS - IMPLICATION OF NUCLEOLAR INVOLVEMENT IN MESSENGER-RNA TRANSPORT (VOL 6, PG 1515, 1995)() RNA IN HEAT)

Transport of mRNA from the nucleus to the cytoplasm plays an important role in gene expression in eukaryotic cells. Ln wild-type Schizosacch aromyces pombe cells poly(A)(+) RNA is uniformly distributed throughou t the nucleoplasm and cytoplasm. However, we found that a severe heat shock blocks mRNA transport in S. pombe, resulting in the accumulation of bulk poly(A)(+) RNA, as well as a specific intron-less transcript, in the nucleoli. Pretreatment of cells with a mild heat shock, which induces heat shock proteins, before a severe heat shock protects the m RNA transport machinery and allows mRNA transport to proceed unimpeded . In heat-shocked S. pombe cells, the nucleolar region condensed into a few compact structures. Interestingly, poly(A)+ RNA accumulated pred ominantly in the condensed nucleolar regions of the heat-shocked cells . These data suggest that the yeast nucleolus may play a role in mRNA transport in addition to its roles in rRNA synthesis and preribosome a ssembly.