Readthrough transcription occurs at the rho dependent signal F1 TIV in suppressor cells.

Suppressor cells infected with bacteriophage f1 yield phage encoded gene IV transcripts longer than those present in the supo host and identical to those found in a rho- host. However, such longer transcripts do not appear in the suppressor-infected cell when, by changing the translation frame of gene IV, the ribosome is not allowed to proceed to the end of the gene IV message and thus to reach the rho dependent transcription terminator f1 TIV. This suggests that ribosome movement beyond the natural gene IV stop codon disturbs the activity of that termination signal.

Biochemical and electron microscopic evidence that cell nucleus negatively controls mitochondrial genomic activity in early sea urchin development.

Enucleated halves of sea urchin eggs obtained by centrifugation contain almost all the mitochondrial population of the egg. Removal of the nucleus followed by parthenogenetic activation stimulates the incorporation of [3H]thymidine into the mitochondrial DNA, whereas no such incorportion is observed in activated whole eggs. The block is not the result of a modification in the permeability of the mitochondrial membrane.

Mitochondrial division in non nucleated sea urchin eggs.

An electron microscopic analysis of non nucleated and parthenogenetically activated sea urchin eggs shows figures that can be interpreted as dividing mitochondria. This is in agreement with our previous observations showing that the egg nucleus negatively controls mitochondrial DNA synthesis.

Synthesis of RNA in isolated nuclei of sea urchin embryos.

It is demonstrated that isolated nuclei of sea urchin embryos are able to incorporate radioactive nucleotides into RNA.Some properties of the incorporation system are described.

Effect of chemical animalization and vegetalization on the synthesis of ribosomal RNA in sea urchin embryos.

Treatment of embryos of Paracentrotus lividus with a concentration of ZnSO which causes animalization, strongly inhibits the initiation of ribosomal RNA synthesis.The vegetalizing agent LiCl does not seem clearly to affect the synthesis of this RNA.

Gene expression in sea urchin development.

Actinomycin D has been administered for various lengths of time and at various concentrations to developing sea urchin embryos. The results obtained support the following suggestions. (1) The shape of respiratory curve up to the mesenchyme blastula stage is not under direct gene control.