In the late L2 and early L3 stages, GFP was expressed in all the Pn.p cells, but by mid to late L3 stages, GFP was largely restricted to the P6.p cell, with some expression in the P5.p and P7.p cell descendants. A similar fusion construct in which the
let-60 3'UTR was replaced by the unregulated
unc-54 3'UTR showed GFP expression in all Pn.p cells. Since the
lin-31 promoter is active in all Pn.p cells, this result demonstrates that the
let-60/RAS 3'UTR is sufficient to downregulate a reporter gene in the non-P6.p cells.