An Analysis of the Effects of Oestrogen Treatment in vivo on the Protein‐Synthetic Activity of Male Xenopus Liver Cell‐Free Systems

A cell‐free protein‐synthesising system has been prepared from the liver of adult male Xenopus laevis which shows several adaptive changes following induction of egg‐yolk protein synthesis by administration of oestradiol‐17βin vivo. The product of the cell‐free system from oestrogen‐treated animals is characterised by elevated incorporation of radioactive serine relative to phenylalanine. This is taken as an indication of the synthesis of phosvitin, which has a high serine content, in vitro. Increased protein‐synthetic activity of Xenopus liver ribosomes following oestrogen treatment can be demonstrated and is maintained after the particles are washed in 0.5 M KCl. This effect of the hormone is also apparent when the ribosomes are first stripped of endogenous mRNA by preincubation and then added to a fresh cell‐free system containing poly (U). It is concluded that oestrogen treatment produces an intrinsic activation of synthetic ability of ribosomes in the liver. Increased ability of ribosomes to translate poly(U) does not result from changes in their ability to bind the polynucleotide, either before or after preincubation. Cell sap from liver of oestrogen‐treated animals shows increased ability to support amino acid incorporation by ribosomes from control or treated animals in vitro. This is not due to enhanced initiation of peptide synthesis or to increased availability of endogenous aminoacyl‐tRNA in vitro. The effects of oestradiol on Xenopus liver are considered in relation to the translational control of protein synthesis by hormones and other agents in a variety of systems.