Reduced stability of RNA coding for yolk polypeptide 3 in Drosophila melanogaster ovary.

In Drosophila three yolk polypeptides (YP1, YP2 and YP3) are synthesized at two sites in the adult female: in the fat body tissue, from which they are transported via the haemolymph to the ovary, and in the ovarian follicle cells which surround the developing oocytes. All three yolk polypeptides are synthesized at equal levels in the fat body. In this paper we show that the steady-state level of YP3 RNA is significantly reduced in the ovary in comparison with the fat body, and that none of the yolk protein genes is amplified either in the fat body or the follicle cells. In order to determine the basis of the reduced level of YP3 RNA in the ovary, which could result from a lower rate of transcription or through a decreased stability of the RNA, we have devised an in vivo method of determining relative rates of gene transcription. In both the fat body and the ovary all three yolk proteins are transcribed at similar rates. Thus we infer that YP3 RNA is destabilised in the ovary, accounting for the reduction in its steady-state level.