intron-containing gene expression

Several nuclear pore-associated factors, including the SUMO-protease Ulp1, have been proposed to prevent the export of intron-containing messen-ger ribonucleoparticles (mRNPs) in yeast. How-ever, the molecular mechanisms of this nuclear pore-dependent mRNA quality control, including the sumoylated targets of Ulp1, have remained uniden-tified. Here, we demonstrate that the apparent ‘pre-mRNA leakage ’ phenotype arising upon ULP1 inacti-vation is shared by sumoylation mutants of the THO complex, an early mRNP biogenesis factor. Impor-tantly, we establish that alteration of THO complex activity differentially impairs the expression of in-tronless and intron-containing reporter genes, rather than triggering bona fide ‘pre-mRNA leakage’. In-deed, we show that the presence of introns within THO target genes attenuates the effect of THO inacti-vation on their transcription. Epistasis analyses fur-ther clarify that different nuclear pore components in-fluence intron-containing gene expression at distinct stages. Ulp1, whose maintenance at nuclear pores depends on the Nup84 complex, impacts on THO-dependent gene expression, whereas the nuclear basket-associated Mlp1/Pml39 proteins prevent pre-mRNA export at a later stage, contributing to mRNA quality control. Our study thus highlights the multi-plicity of mechanisms by which nuclear pores con-tribute to gene expression, and further provides the first evidence that intronic sequences can alleviate early mRNP biogenesis defects