Control of Protein Synthesis in Cuboidal Rat Mammary Epithelial Cells in Culture

Abstract

The cuboidal rat mammary tumor cell line, Rama 25, spontaneously converts to elongated cells during culture. The polypeptides synthesised by the 2 morphological forms are compared by 2-dimensional polyacrylamide gel electrophoresis. In addition to major changes in the intermediate filament proteins, there are 2 abundant acidic polypeptides of MW 9000 and 15,500, which are synthesised by the elongated cells but which are not detectable in the cuboidal cells. When mRNA preparations isolated from the cuboidal and elongated cells are translated in the reticulocyte lysate, the patterns of radioactive products resemble the patterns of polypeptides synthesised in the intact cells. Translation products corresponding to the 9000-MW and 15,500-MW polypeptides are synthesised when mRNA from elongated cells is translated, but are not synthesized when mRNA from cuboidal cells is translated. The appearance of these 2 proteins may represent a change in gene expression between the 2 cell types and control is apparently exerted prior to mRNA translation.