Four tandem copies of the 260bp twi proximal element (PE) (located between -440 and -180 relative to the twi promoter), followed by twi sequence from -180 to +160bp relative to the transcription start site, are fused upstream of lacZ.
Strong expression of EcollacZ spanningthe 12-14 ventral-most cells of the embryo.
In embryos at cellular blastoderm, expressed at high levels in the ventralmost 12-14 cells, with sharp boundaries at lateral borders.