Abstract
Monoclonal antibodies were used to study the structure and the biosynthesis of the rabbit progesterone receptor. Proteins in nonfractionated uterine cytosol were submitted to gel electrophoresis in denaturing conditions, transferred onto nitrocellulose, and reacted with monoclonal antireceptor antibodies and 125I-protein A. A single 110,000-dalton protein was observed when precautions were taken during homogenization of the uteri and protease inhibitors used. Smaller forms of receptor (essentially of 79,000 daltons but also of 72,000 and in some experiments of 64,000 daltons) were present when these precautions were not observed and thus probably arose from artifactual proteolysis of receptor. When poly(A)+ RNA from rabbit uterus was translated in a reticulocyte lysate and the radioactive proteins precipitated by the antireceptor monoclonal antibodies, a radioactive protein of 110,000 daltons was also observed. Further evidence that this protein was the product of the translation of progesterone receptor mRNA was obtained by precipitation and immunoaffinity purification with several antireceptor monoclonal and polyclonal antibodies, inhibition of immunoprecipitation by purified receptor and its absence in a receptor-poor tissue (liver). Estrogen treatment is known to increase the concentration of progesterone receptor. RNA translation experiments showed that this effect is due to an increase in the concentration of receptor mRNA. The size of this messenger RNA was studied by sucrose gradient ultracentrifugation, followed by mRNA translation, and specific immunoprecipitation: progesterone receptor mRNA was found by this method to sediment at 20 S.
Highlights
Monoclonal antibodies wereused to study the struc- concluded that a similar subunit composition exists for the ture and the biosynthesis of the rabbit progesterone human progesterone receptor [5]
When precautions were taken during homogenization The mechanisms of biosynthesis of steroid receptors have of the uteri and protease inhibuitsoerds
When poly(A)+RNA from rabbit uterus was translated in a reticulocyte lysate and the radioactive proteins precipitated by the antireceptor monoclonal antibodies, a radioactive proteinof 110,000 daltons was observed. Further evidence that this protein was the productof the translationof progesterone receptor mRNA was obtained by precipitation and immunoaffinity purification with several antireceptormonoclonal and polyclonal antibodies, inhibition of immunoprecipitation by purified receptor andits absence in a
Summary
EVIDENCE FOR A SINGLE STEROID-BINDING SUBUNIT AND CHARACTERIZATION OF RECEPTOR mRNA*. When poly(A)+RNA from rabbit uterus was translated in a reticulocyte lysate and the radioactive proteins precipitated by the antireceptor monoclonal antibodies, a radioactive proteinof 110,000 daltons was observed. Further evidence that this protein was the productof the translationof progesterone receptor mRNA was obtained by precipitation and immunoaffinity purification with several antireceptormonoclonal and polyclonal antibodies, inhibition of immunoprecipitation by purified receptor andits absence in a. We have recently succeeded in preparing monoclonal antibodies having a high affinity for the rabbit progesterone receptor [11] With this tool we have studied by immunoblot methods [12], the size, andthestructure of the receptor 3howing that it consists of a single subunit of 110,000daltons, smaller fragments arisingprobably from proteolytic degradation.
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