The regulation of translation by the 5′ untranslated region of Xenopus c-myc I mRNA during early development

The translational efficiency of chloramphenicol acetyltransferase (CAT) mRNA containing 5′ untranslated region (UTR) sequences of Xenopus c-myc I mRNA was examined in the Xenopus oocyte and early embryo. In contrast to their reduced translation in the oocyte, CAT mRNAs containing 5′ UTR sequences located between the c-myc I P₀ and P₂ promoters translate as efficiently as CAT mRNA controls when injected into early embryos. This pattern of differential regulation of c-myc I translation is similar to that observed for mouse c-myc 5′ UTR-containing CAT transcripts during Xenopus oogen-esis and early embryogenesis [Lazarus, P., Parkin, N. & Sonenberg, N. (1988). Oncogene, 3, 517-521]. Ooctyespecific translational inhibition was not observed for CAT mRNAs containing c-myc I 5′ UTR sequences located 3′ of the P₂ promoter. No significant alteration in c-myc I 5′ UTR/CAT mRNA stability was observed in the oocyte as compared with CAT mRNA controls. The significance of this promoter-dependent translational regulation with respect to c-myc expression and early Xenopus development is discussed.