FIG. 9.

Model for genetic switch of mpl genes by promoter inversion. The upstream intergenic regions of the p42 genes are illustrated. The open arrows represent promoter sequences and their directions. The short solid arrows represent 12-bp inverted repeats (IR). The hatched boxes represent terminator-like sequences (16-bp inverted repeats). When the promoter is in the OFF orientation (GTU), an active terminator is formed. The inversion between 12-bp inverted-repeat sequences changes the promoter direction from OFF to ON and splits the terminator sequence. RNA transcripts from the promoter and from upstream are represented by thin solid arrows.