Key RNA-binding protein involved in the formation of polar-growing hyphae which is essential for infection by the plant pathogen (PubMed:15643068, PubMed:17105762, PubMed:19494833). During filamentation, assembles into particles that shuttle bidirectionally along microtubules to both poles (PubMed:17105762, PubMed:19494833, PubMed:30738139). The RRM4 transport particles are part of the endosomal mRNP transport that regulates polarity of the infectious hyphae by transporting distinct mRNAs encoding, for example, the ubiquitin fusion protein UBI1, the small G protein RHO3, or the septin CDC3, from the nucleus to cell poles (PubMed:17105762, PubMed:19494833, PubMed:22357951, PubMed:24355572, PubMed:25985087, PubMed:30738139). Recognizes a broad spectrum of cargo mRNAs and precisely binds at stop codons, which constitute landmark sites of translation, suggesting an intimate connection of mRNA transport and translation (PubMed:30552148). Binds also to the specific binding motif UAUG of cargo mRNAs via its third RRM (PubMed:30552148). Plus-end-directed KIN3, a kinesin-3 type motor, mediates anterograde transport of RRM4-containing mRNPs whereas split dynein DYM1-DYN2 functions in retrograde movement of mRNPs (PubMed:22357951). Part of large ribonucleoprotein complexes (mRNPs) containing RNA-binding proteins RRM4 and PAB1, endosome-binding protein UPA1, core scaffold protein UPA2 and associated factor GRP1 (PubMed:17105762, PubMed:19494833, PubMed:22357951, PubMed:31338952, PubMed:30738139). Interacts (via PABC domain) with UPA1 (via PAM2 domain) (PubMed:25985087). Assembles into particles that shuttle along microtubules to both poles (PubMed:17105762, PubMed:19494833). Shuttles with RAB5A-positive endosomes along microtubules (PubMed:22357951, PubMed:25985087). The RRM1, RRM3 and PABC domains are important for RNA_binding and polar growth (PubMed:17105762, PubMed:19494833). RRM3 recognizes the specific binding motif UAUG of cargo mRNAs (PubMed:30552148). Reduces filamentous growth and virulence (PubMed:15643068). Disturbs polar growth of filaments (PubMed:17105762, PubMed:25985087). Belongs to the polyadenylate-binding protein type-1 family.