Role of the SPF27 homologue Num1 in splicing and transport in Ustilago maydis
Final Report Abstract
The conserved NineTeen protein complex (NTC) is an integral subunit of the spliceosome and required for intron removal during pre-mRNA splicing. The complex associates with the spliceosome and participates in the regulation of conformational changes of core spliceosomal components, stabilizing RNA-RNA- as well as RNA-protein interactions. In addition, the NTC is involved in cell cycle checkpoint control, response to DNA damage or formation and export of mRNP-particles. The major finding of our study is that Num1, one of the core components of the conserved spliceosome-associated NTC in Ustilago maydis, is involved in cytoplasmic trafficking processes. We show that Num1 is an integral subunit of the spliceosome and required for intron removal during pre-mRNA splicing on a global scale. Within the NTC at least one of the functions of Num1 is to stabilize the complex. In line with its phenotype, Num1 interacts with proteins complexes involved in DNA-repair/chromosomal maintenance, but also with the regulatory subunit of the proteasome. A unexpected, novel finding is its interaction with several proteins with putative functions in cytoplasmic transport processes, as Kin1, tubulin 1 and tubulin 2. Similar phenotypes with respect to filamentous and polar growth, vacuolar morphology, as well as the motility of early endosomes corroborate the genetic interaction between Num1 and Kin1. The num1 mutation affects cytoplasmic mRNA transport, and the protein interacts with components of the mRNA export and transport maschinery. Our data implicate a previously unidentified connection between a component of the splicing machinery and cytoplasmic transport processes. The connection of Num1 to the cytoplasmic transport machinery is further supported by its interaction with Nma1, an orphan protein only present in Ustilago and its close relatives. nma1 deletion leads to a phenotype that resembles in part the ∆num1 deletion. The protein localizes in motile spots on microtubles in the cytoplasm, accumulates in MTOCs and during mitosis on mitotic spindles. The association of Nma1 with components of the CORVET complex suggests a function in vesicle sorting or identity. As vesicular transport has recently been shown to be required spindle formation during mitosis, we are currently investigating the function of Nma1 within this scenario.
Publications
- (2014). The SPF27 homologue Num1 connects splicing and kinesin 1-dependent cytoplasmic trafficking in Ustilago maydis. PLoS Genet 10, e1004046
Kellner, N., Heimel, K., Obhof, T., Finkernagel, F., and Kämper, J.
