Control of protein synthesis in cuboidal rat mammary epithelial cells in culture. Changes in gene expression accompany the formation of elongated cells.

The cuboidal rat mammary tumour cell line, Rama 25, spontaneously converts to elongated cells during culture. The polypeptides synthesised by the two morphological forms are compared by two-dimensional polyacrylamide gel electrophoresis. In addition to major changes in the intermediate filament proteins, there are two abundant acidic polypeptides of molecular weights 9000 and 15500, 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-Mr and 15500-Mr polypeptides are synthesised when mRNA from elongated cells is translated, but are not synthesised when mRNA from cuboidal cells is translated. Evidence is presented that the appearance of these two proteins represents a change in gene expression between the two cell types and that control is exerted prior to mRNA translation.