The estradiol receptor of lamb endometrium, translocated to nuclei in útero and extracted with micrococcal nuclease at 2-4 °C, was compared under low salt conditions to the "native" 8S and to partially proteolyzed cytosol receptor.The degree of extraction of the receptor was roughly parallel to the proportion of digested chromatin and to the yield of extracted DNA. After extensive digestion of chromatin, which produced up to 10% perchloric acid soluble DNA and more nucleosome monomer than dimer, up to 80% of the nuclear receptor was extracted under low ionic strength and subse-

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Glucocorticoid receptors (RG) and mammary tumor virus (MM-TV) DNA sequences were extracted by micrococcal nuclease digestion from the nuclei of C3H mouse mammary tumor cells in order to specify their relative distribution in chromatin. RG was labelled and translocated into the nuclei by incubating cells with 3H Dexamethasone (3H Dex). The purified nuclei were then treated at 2 degrees C with micrococcal nuclease. Three chromatin fractions were successively obtained: an isotonic extract (ne3H1), ahypotonic extract (ne2) and the residual pellet (P). The Dex-RG complexes were measured by the hydroxyapatite technique. The MMTV DNA sequences were titrated by molecular hybridization with an excess of MMTV radioactive cDNA probe. Up to 75% of the nuclear 3H Dex and the MMTV radioactive cDNA probe. Up to 75% of the nuclear 3H Dex and MMTV DNA sequences were extracted in a concentration dependent manner while only 10-15% of nucleic acids became soluble in 10% perchloric acid. The extracted 3H Dex-RG complex was found to be partly bound to soluble chromatin and partly free. The free complex displayed similar sedimentation constants (4S, 7S) and DNA binding ability to the cytosol receptor. The 3H Dex-RG complexes were 2 to 8 fold more concentrated in ne1, which is known to be enriched in active chromatin, than in ne2. Conversely, the concentration of MMTV DNA sequences per microgram DNA was the same in the three nuclear fractions. These results suggest that the Dex-RG complexes are concentrated in an active fraction of chromatin. We propose that, among the 20-30 copies of MMTV genes per haploid genome, only a small proportion are transcribed or regulated.

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L'auteur passe en revue les principaux travaux récents sur la relation d'arbitrage et souligne les incertitudes qui entourent cette notion et son utilisation pour la prise de décision. Suite à une brève présentation de résultats obtenus à partir d'un modèle plus complexe que les traditionnelles relations bi-dimensionnelles d'arbitrage, l'auteur s'attache aux conséquences pour la politique économique de la mise en question de la stabilité et de l'existence même de cette relation. Il souligne alors l'importance des politiques de gestion de la demande et compare les coûts respectifs de l'inflation et du sous-emploi.