The degree of similarity of ribosomal proteins from various species or from various organs within a given species is not clearly known. Using two‐dimensional polyacrylamide‐gel electrophoresis, we have compared liver ribosomal proteins from adult chicken, adult rabbit, fetal and adult calf and ewe. In the rabbit, we also studied ribosomal proteins from kidney, caecal appendix and reticulocytes. In all the cases which we investigated, more than 60 strongly basic proteins are visible. For one given organ, ribosomal proteins do not vary according to the stage of differentiation. Within one given species, there exists few differences from one tissue to another. From one species to another, there are also few differences but the unexpected resemblance of most of the proteins is remarkable.

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