MESSENGER-RNA TRANSPORT IN YEAST - TIME TO REINVESTIGATE THE FUNCTIONS OF THE NUCLEOLUS

Nucleocytoplasmic transport of mRNA is vital to gene expression and ma y prove to be key to its regulation. Genetic approaches in Saccharomyc es cerevisiae have led to the identification of conditional mutants de fective in mRNA transport. Mutations in approximately two dozen genes result in accumulation of transcripts, trapped at various sites in the nucleus, as detected by in situ hybridization. Phenotypic and molecul ar analyses of many of these mRNA transport mutants suggest that, in y east, the function of the nucleolus is not limited to the biogenesis o f pre-ribosomes but may also be important for transport of poly(A)(+) RNA. A similar function of the animal cell nucleolus is suggested by s everal observations.