title: The RNA-binding protein Rrm4 is essential for efficient secretion of endochitinase Cts1.
abstract: Long-distance transport of mRNAs is crucial in determining spatio-temporal gene expression in eukaryotes. The RNA-binding protein Rrm4 constitutes a key component of microtubule-dependent mRNA transport in filaments of Ustilago maydis. Although a number of potential target mRNAs could be identified, cellular processes that depend on Rrm4-mediated transport remain largely unknown. Here, we used differential proteomics to show that ribosomal, mitochondrial, and cell wall-remodeling proteins, including the bacterial-type endochitinase Cts1, are differentially regulated in rrm4Δ filaments. In vivo UV crosslinking and immunoprecipitation and fluorescence in situ hybridization revealed that cts1 mRNA represents a direct target of Rrm4. Filaments of cts1Δ mutants aggregate in liquid culture suggesting an altered cell surface. In wild type cells Cts1 localizes predominantly at the growth cone, whereas it accumulates at both poles in rrm4Δ filaments. The endochitinase is secreted and associates most likely with the cell wall of filaments. Secretion is drastically impaired in filaments lacking Rrm4 or conventional kinesin Kin1 as well as in filaments with disrupted microtubules. Thus, Rrm4-mediated mRNA transport appears to be essential for efficient export of active Cts1, uncovering a novel molecular link between mRNA transport and the mechanism of secretion.
authors.affiliation: Heinrich-Heine University Düsseldorf, Institute for Microbiology, Düsseldorf, Germany.
authors.forename: Janine
authors.initials: J
authors.lastname: Koepke
authors.forename: Florian
authors.initials: F
authors.lastname: Kaffarnik
authors.forename: Carl
authors.initials: C
authors.lastname: Haag
authors.forename: Kathi
authors.initials: K
authors.lastname: Zarnack
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Luscombe
authors.forename: Julian
authors.initials: J
authors.lastname: König
authors.forename: Jernej
authors.initials: J
authors.lastname: Ule
authors.forename: Ronny
authors.initials: R
authors.lastname: Kellner
authors.forename: Dominik
authors.initials: D
authors.lastname: Begerow
authors.forename: Michael
authors.initials: M
authors.lastname: Feldbrügge
mesh_terms: D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D002688:Chitinases / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism / Q000502:physiology*; D055786:Gene Knockout Techniques; D008969:Molecular Sequence Data; D010802:Phylogeny; D011485:Protein Binding; D021381:Protein Transport; D012323:RNA Processing, Post-Transcriptional; D034443:RNA Transport; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012261:Ribonucleoproteins / Q000378:metabolism; D057825:Two-Dimensional Difference Gel Electrophoresis; D014588:Ustilago / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D005656:Fungal Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; D002688:Chitinases