Characterization of full-length cDNA for Xenopus IRBP. A) cDNA XenB1 isolated under low stringency conditions , was used here to screen under high stringency a Xenopus stage 45 swimming tadpole cDNA library. B) This screen led to the isolation of Xen10a, a full-length Xenopus IRBP cDNA whose sequence is shown in Figure 2. Arrows represent individual sequencing runs. The solid bars indicate coding regions. E, EcoR1; X, XbaI.