Eukaryotic ribosomal proteins: the number of proteins in the subunits and their isoelectric points.

Today the number of proteins [l-5] in eukaryotic ribosomal subunits as well as their molecular weights [6] are fairly well determined. Many of these proteins are also isolated and purified [3]. Just like histones, ribosomal proteins are very basic. Both kinds occur naturally in combination with nucleic acids: so it is likely that electrical charges play an important part in the association of these proteins to their respective nucleic acids. As a step towards the understanding of this association it seems therefore necessary to evaluate the electrical charges on the proteins. This may be done globally by measuring their isoelectric points. As the isolation of individual ribosomal proteins is an elaborate and time consuming process, the two-dimensional electrophoresis method of Kaltschmidt [7], which does not require isolation of individual proteins, is used to this end.