Translation of the mRNA for rabbit uteroglobin in cell-free systems. Evidence for a precursor protein.

Uteroglobin, an hormonally induced protein composed of two similar subunits, represents around 50% of the proteins synthesized and secreted into the uterine lumen of rabbits treated sequentially with estradiol and progesterone. The endometrium of these animals was used as a source for the isolation of the mRNA for uteroglobin. Poly(A)-rich RNA, extracted from purified polysomes with phenol chloroform and isolated on oligo(dT)-cellulose columns, contains one fourth of the total protein coding activity of the endometrium. Between 20--25% of the polypeptides synthesized by this RNA in cell-free systems derived from Krebs II ascites cells or wheat germs react with a monospecific antiserum prepared in guinea pigs against uteroglobin. The material bound to the antibody was identified as a precursor of uteroglobin according to the following criteria. 1. The product synthesized in vitro can be displaced from the complex with the specific immunoglobulin by purified uteroglobin. 2. Analysis of the immunoprecipitate on polyacrylamide gels containing urea and dodecylsulfate demonstrate the existence of a single labelled polypeptide with an apparent molecular weight larger than the uteroglobin subunits. 3. The tryptic digest of this polypeptide, labelled in vitro with [3H]lysine, shares seven peptides with mature uteroglobin labelled with the same amino acid in perfused uteri, and exhibits and additional peptide not present in uteroglobin. 4. Injection of the same mRNA preparation into Xenopus oocytes results in the production of uteroglobin. The endometrium of intact animals treated with estradiol alone also contains the same mRNA bound to polysomes but in a smaller proportion, indicating that the progesterone-induced synthesis of uteroglobin is accompanied by an accumulation of the specific mRNA in the polysomes.