DEGRADATION OF MATERNAL STRING MESSENGER-RNA IS CONTROLLED BY PROTEINS ENCODED ON MATERNALLY CONTRIBUTED TRANSCRIPTS

In Drosophila, maternal string mRNAs are stable for the first few hour s of development, but undergo specific timed degradation at the cellul arisation stage. To determine whether the proteins that control this d egradation are maternally or zygotically transcribed, we have used in situ hybridisation to determine the fate of maternal string transcript s in mutant embryos which lack individual chromosome arms. Our data in dicate that maternal string mRNA persists for the normal period in all these mutants. Using alpha-amanitin to inhibit zygotic transcription we have shown that degradation of maternal mRNA is unaffected. Therefo re, the proteins required to activate the degradation of string mRNA a re encoded on a maternally contributed mRNA. We discuss possible model s to explain the degradation pathway.