Nuclear mRNA accumulation causes nucleolar fragmentation in yeast mtr2 mutant

Tatsuhiko Kadowaki*, Midori Hitomi, Shaoping Chen, Alan M. Tartakoff

*Corresponding author for this work

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We have identified a set of genes that affect mRNA transport (mtr) from the nucleus to the cytoplasm of Saccharomyces cerevisiae. One of these genes, MTR2, has been cloned and shown to encode a novel 21-kDa nuclear protein that is essential for vegetative growth. MTR2 shows limited homology to a protein implicated in plasmid DNA transfer in Escherichia coli. PolyA+RNA accumulates within the nucleus of mtr2-1 in two to three foci at 37°C, mRNA, tRNA, and rRNA synthesis continue as do pre-mRNA splicing, tRNA processing, and rRNA export at 37°C. Under these conditions the polyA tail length increases, and protein synthesis is progressively inhibited. Nucleolar antigens also redistribute to two to three nuclear foci at 37°C, and this redistribution depends on ongoing transcription by RNA polymerase II. Surprisingly, these foci coincide with the sites of polyA+RNA accumulation. Comparable colocalization and dependence on RNA polymerase II transcription is seen for the mtr1-1 mutant. The disorganization of the nucleolus thus depends on mRNA accumulation in these mutants. We discuss the possible functions of MTR2 and the yeast nucleolus in mRNA export.

Original languageEnglish
Pages (from-to)1253-1263
Number of pages11
JournalMolecular Biology of the Cell
Issue number11
Publication statusPublished - Nov 1994
Externally publishedYes

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