Masking mRNA from translation in somatic cells.

We present evidence for a role for Y-box proteins in both mRNA transcription and translation. We have expressed an oocyte-specific RNA-binding protein (FRGY2) in somatic cells. This protein is normally found together with mRNA in large amounts within the masked maternal mRNA storage particles of Xenopus laevis oocytes. Masked maternal mRNA is believed to be translationally repressed during oogenesis and is stored within ribonucleoprotein storage particles for subsequent use during embryogenesis. Surprisingly, FRGY2 is not only found to direct the accumulation of mRNA from promoters containing binding sites for the protein but also to selectively repress translation of the same mRNA. Thus, the role of FRGY2 in the transcription and storage of maternal mRNA is similar to that of the transcription factor TFIIIA in the transcription and storage of 5S rRNA from the oocyte type 5S rRNA genes.