TEMPORAL CONTROL OF GENE-EXPRESSION FROM ENDOGENOUS AND EXOGENOUSLY-INTRODUCED DNAS IN EARLY EMBRYOGENESIS OF XENOPUS-LAEVIS

We review here our studies on temporal control of the expression of ge nes in zygotic nucleus and of exogenously introduced genes in Xenopus embryos. For zygotic gene expression, our studies have revealed that m RNA synthesis, tRNA synthesis and rRNA synthesis initiates at the clea vage stage, MBT stage and late blastula stage, respectively. We also b riefly summarize here results of the effects of weak bases on rDNA exp ression, nucleo-cytoplasmic transport and polysomal mobilization of ne wly-synthesized RNAs. For exogenously injected genes expression our da ta have shown the control of the expression by the promoter and config uration (circular or linear) of the injected DNAs but not necessarily by cellular changes that take place during the midblastula transition (MBT).