A 650-bp region between 1.5 and 0.9 kb upstream of
egl-18a, when fused with
pes-10 basal promoter, was sufficient for moderate levels of GFP expression in the developing vulva. Additional analyses revealed that the downstream half (350 bp) of the 650-bp region was sufficient for vulval expression. Neither half of the 350-bp region (pYB16 and pYB19) resulted in vulval expression above the background, which suggests that both halves of the
f350-bp region are important for vulval expression. The removal of this
f350-bp regulatory element in nT1 animals is likely to result in substantially reduced vulval expression of the
egl-18 and
elt-6 GATA factors.