Fig. 6. CDL-1 interacts with the stem-loop structure in the 3'-UTR of core-histone mRNA. (A) The yeast three-hybrid system (SenGupta et al., 1996) was used to test the RNA binding specificity of CDL-1. The assay is schematically shown. (B) Structure of the two stem-loop RNAs used in the experiments. wtRNA: the conserved stem-loop sequence in the 3'-UTR of C. elegans core histone mRNA. rvRNA: the sequence with a reversed stem-loop. (C) RNA-binding activity of CDL-1 protein as assayed by ß-galactosidase activity. IRE (Iron Response Element) and IRP (Iron Response Protein) were used as a pair of positive controls (SenGupta et al., 1996). (D) Activation of HIS3. Transformants indicated in C were streaked on –His plates containing 5 mM 3-aminotriazol.