RNA-binding protein that binds to a cis-localization element or zipcode, within the 5'-CDS of prolamine RNA (PubMed:20217123, PubMed:24682961). Binds strongly to glutelin mRNA, particularly to 3'-UTR and zipcode RNA (PubMed:24682961). Recognizes and binds to glutelin zipcode RNA, which is required for proper mRNA localization to cisternal endoplasmic reticulum (PubMed:24682961). Exhibits strong binding activity to a glutelin intron sequence and may participate in mRNA splicing (PubMed:24682961). Required for the correct localization of glutelin and prolamine mRNA in endosperm cells during grain development (PubMed:30190374). RBP-P and RBP-L form a quaternary complex with the membrane trafficking factors NSF and RAB5A (PubMed:32471860). This quaternay complex carries glutelin mRNAs for active transport on endosomes to the cortical endoplasmic reticulum membrane, and enables endosome-mediated glutelin mRNA transport in endosperm cells (PubMed:32471860). Forms homodimers (PubMed:30190374). Interacts with RBP-L and RBP-208 (PubMed:30190374). Interacts with NSF (PubMed:32471860). During flowering and seed development, expressed very weakly at 3 days after flowering (DAF) (at protein level) (PubMed:24682961). Expression increases until 9 DAF and remains relatively steady until a sharp decline 23 DAF (at protein level) (PubMed:24682961). Extended N-terminus.