Repression and turnover pattern fushi tarazu RNA in the early Drosophila embryo.

Embryonic expression of transcripts from the Drosophila gene fushi tarazu (ftz) progresses through a series of spatial patterns, culminating in a seven-banded pattern at the cellular blastoderm stage. We studied the generation of this pattern using inhibitors of RNA synthesis (alpha-amanitin) and protein synthesis (cycloheximide). Injections of alpha-amanitin revealed that ftz RNA turns over extremely rapidly in the embryo, and we think that this may be essential to effect rapid changes in ftz RNA patterns. Injections of cycloheximide added to the normal domains of ftz expression, creating novel expression patterns that were dependent on the time of injection. These novel patterns suggest that two superimposed systems of repression establish the normal, seven-banded pattern of ftz expression. One system sets up a banded pattern over the entire length of the embryo, and the other restricts actual expression to the middle portion of the embryo.