Discrete sequence elements control posterior pole accumulation and translational repression of maternal cyclin B RNA in Drosophila.

The concentration of cyclin B transcripts at the posterior pole of the Drosophila oocyte occurs at a late stage of oogenesis and is dependent on the sequence in the 3' untranslated part of the RNA. These transcripts become incorporated into the pole cells of the developing embryo and persist through a subsequent period of embryogenesis in which these cells are not dividing. We show that RNA injected into the posterior cytoplasm of syncytial embryos accumulates in the pole cells if it contains sequences present in the 3' untranslated region of maternal cyclin B transcripts. The injected RNA is not translated until a point prior to the resumption of mitosis by these cells, once they have become incorporated into the gonads. Zygotic transcription directed from the cyclin B promoter does not begin in the pole cells until the first instar larva has hatched. Deletion of a small sequence element from the 3' untranslated region of an epitope tagged cyclin B RNA does not affect its posterior accumulation but results in its premature translation.