Abstract
Most Cryptococccus neoformans genes are interrupted by introns, and alternative splicing occurs very often. In this study, we examined the influence of introns on C. neoformans gene expression. For most tested genes, elimination of introns greatly reduces mRNA accumulation. Strikingly, the number and the position of introns modulate the gene expression level in a cumulative manner. A screen for mutant strains able to express functionally an intronless allele revealed that the nuclear poly(A) binding protein Pab2 modulates intron-dependent regulation of gene expression in C. neoformans. PAB2 deletion partially restored accumulation of intronless mRNA. In addition, our results demonstrated that the essential nucleases Rrp44p and Xrn2p are implicated in the degradation of mRNA transcribed from an intronless allele in C. neoformans. Double mutant constructions and over-expression experiments suggested that Pab2p and Xrn2p could act in the same pathway whereas Rrp44p appears to act independently. Finally, deletion of the RRP6 or the CID14 gene, encoding the nuclear exosome nuclease and the TRAMP complex associated poly(A) polymerase, respectively, has no effect on intronless allele expression.
Highlights
Introns, discovered in 1977, are genomic sequences that are removed from the corresponding RNA transcripts of genes [1]
We demonstrate that introns modulate gene expression in a cumulative manner
We identify a nuclear poly(A) binding protein (Pab2p) as implicated in the intron-dependent control of gene expression in C. neoformans
Summary
Introns, discovered in 1977, are genomic sequences that are removed from the corresponding RNA transcripts of genes [1]. The presence of introns and their splicing by the RNA-protein complex named spliceosome [2] affect gene expression by different means [3] including transcription, polyadenylation, mRNA export, mRNA localisation, translation efficiency and the rate of mRNA decay (see [4] for review). Most eukaryotic genes contain introns the proportion of genes containing introns is highly variable between organisms. Whereas 92% and 78% of the genes in human and plant genomes contain introns, respectively, [5,6] introns are found in only 5% of the genes in the yeast Saccharomyces cerevisiae [7]. The influence of introns on gene expression differs from one organism to another and from one gene to another
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