Prion-like protein required for the formation of Balbiani body (electron-dense aggregates in the oocyte) and germ plasm assembly, and for the establishment of oocyte polarity during early oogenesis (PubMed:18582455, PubMed:19249209). Mobility and aggregation properties are improved by tudor domain-containing protein tdrd6 through interaction with dimethylated arginines Tri-RG domains (PubMed:30086300). Establishes oocyte polarity through interactions with RNA-binding proteins rbpms2 and dazl, initiating a positive feedback loop amplification mechanism in the Balbiani body (PubMed:24496621). Interaction of BUC protein and mRNA with rbpms2 and dazl is required to mediate Balbiani body formation (PubMed:24496621). Involved in recruitment of germ plasm to embryonic cleavage furrows and dorsoventral patterning through interaction with Kinesin-1/KIF5BA (PubMed:26253407). Specifically interacts (when methylated) with tdrd6 (via Tudor domain); interaction is responsible for recruitment of different protein complexes to germ plasm (PubMed:30086300). Interacts with rbpms2 and dazl; interaction mediates Balbiani body formation (PubMed:24496621). Interacts with kif5ba; interaction leads to buc enrichment at the embryonic cleavage furrows and mediates dorsoventral patterning (PubMed:26253407). Localizes to nuage (a peri-nuclear protein-RNA aggregate that associates closely with mitochondria), the Balbiani body during oogenesis, and in the germ plasm upon fertilization (PubMed:19249209, PubMed:30086300). Accumulates at embryonic cleavage furrows (PubMed:26253407). Expressed exclusively in the ovary, and protein localizes to the Balbiani body during oogenesis and with the germ plasm during early embryogenesis (PubMed:19249209). Accumulates at embryonic cleavage furrows (PubMed:26253407). The dimethylated RG motifs (RG[X0-4]RG[X0-4]RG) motif mediates interaction with TDRD6 and is required for Balbiani body formation. Symmetric dimethylarginine modification promotes interaction with tdrd6. Mutant fails to form Balbiani body, and vegetal mRNAs are not localized in oocytes.