The posttranscriptional machinery of Ustilago maydis

Eukaryotic gene expression begins with transcription and maturation of mRNAs in the nucleus and ends with their translation and degradation in the cytoplasm. Here, we present an inventory of the posttranscriptional machinery of Ustilago maydis that is based on the recently sequenced genome and its comprehensive manual annotation. We used the detailed knowledge available for Saccharomyces cerevisiae and higher eukaryotes to predict posttranscriptional components in this plant pathogen. The comparison to S. cerevisiae revealed that most core components are shared. Both fungi belong to the small group of organisms lacking components of the RNAi machinery. However, a striking difference exists at the level of splicing. U. maydis harbors substantially more intron-containing genes and this correlates with the presence of numerous splice components with human orthologues that are absent or less conserved in S. cerevisiae. In particular, U. maydis contains three out of four core proteins of the exon junction complex, which marks spliced exons and is involved in cytoplasmic mRNA transport. In this context, it is also remarkable that the U. maydis genome displays components involved in microtubule- rather than actin-dependent mRNA transport. Thus, U. maydis might serve as an attractive model system to gain novel insights into posttranscriptional processes.