In Vitro Translation of Messenger RNA for a Uteroglobin-Like Protein from Rabbit Lung

The rabbit uterine protein, uteroglobin has been reported to be present in several other tissues, including the lung. To determine whether the uteroglobin gene is expressed in tissues other than the uterus, the messenger RNA (mRNA) activity of rabbit lung has been studied by translation in vitro in a cell-free protein synthesizing system derived from wheat germ. The poly A-rich RNA contained a specific mRNA whose translation product was precipitable by uteroglobin antibodies purified by affinity chromatography. The lung cell-free product gave a single band on radioautography after polyacrylamide gel electrophoresis under denaturing conditions. The immunoprecipitable radioactivity was completely displaced by authentic uteroglobin and fell to background levels when the specific antibodies were replaced by normal goat serum. In contrast to the uterus, the proportion of lung poly A-rich mRNA accounted for by the specific mRNA for the uteroglobin-like protein was not different between the nonpregnant state and Day 4 of pregnancy. The lung mRNA coded for a protein identical in size to the product of translation of uteroglobin mRNA from the uterus and both products were approximately 1200 daltons larger in molecular weight than authentic uteroglobin. The lung is thus established as a site of synthesis of a uteroglobin-like protein, which may be a common product of secretory epithelium in the rabbit.