Has a dual function in oocytes: as a DNA-binding protein, binds to the Y-box sequence (CTGATTGGCCAA) in the promoters of target genes to stimulate transcription. May also function at CCAAT-containing promoters that lack the consensus Y-box sequence. Also binds mRNA to promote accumulation of the transcripts it contributes to produce. Possibly forms a heterodimer with p54 in the 6S and 15S mRNA-binding particles. The principle component of multiple messenger ribonucleoprotein (mRNP) complexes. Component of a ribonucleoprotein (RNP) complex, composed at least of elavl1/elrA and/or elavl2/elrB, igf2bp3/vg1RBP, ddx6/Xp54, ybx2/frgy2, lsm14b/rap55b and, in a subset of RNP complexes, stau1/staufen. Component of a ribonucleoprotein (RNP) complex, at least composed of lsm14a/rap55a, ybx2/frgy2, ddx6/Xp54 and eif4enif1/4E-T. Does not appear to directly bind lsm14a/rap55a. Component of a ribonucleoprotein (RNP) complex, at least composed of cpeb1, lsm14b/rap55b, ddx6/Xp54, ybx2/frgy2, pat1/P100, eif4enif1/4E-T and eif4e1b. Interaction with cpeb1 is RNA-dependent. Either free or associated with ribonucleoprotein particles. In adults, expression is restricted to the ovary and testis. Expressed maternally. Phosphorylation activates in vitro RNA binding. PubMed:2247479 report a decline in expression during oogenesis, but PubMed:1729676 show expression is maintained at a high level throughout oogenesis.