[Properties of ribosomes of normal and tumor cells (author's transl)]

On the basis of results showing that the extent and direction of protein biosynthesis essential for cell growth and cell differentiation can be regulated, aside from the transcription level, also on the level of ribosomes (translation), the main results of various properties of ribosomes from normal and tumor tissues are described. The main established difference between the two tissues concerns the organization and localization of the ribosomes within the cell. In tumors, polysomes and inactive dimers and monomeric particles are encountered in considerable amounts freely in the cytosol, i.e. not attached to the membranes. Furthermore, the polysomal profile of tumor cells compared with the normal tissue is characterized by a shift towards fractions with lower sedimentation coefficients. Monomeric ribosomes were not found to differ in physical and chemical properties. In smaller oligonucleotide fragments of ribosomal RNA, differences in the frequency of certain dinucleotides appear likely. Hybridization-competition experiments with DNA do suggest, however, that the ribosomal RNA from tumors is being synthesized at the same cistrons as ribosomal RNA from normal tissues, thus proving its overall sequence homology. Electrophoretic and immunologic methods have not so far revealed any clear differences in the properties of ribosomal proteins from normal and tumor tissues. In in-vitro systems, ribosomes from various tumors show approximately the same incorporation rates for amino acids as ribosomes from normal tissues. The enhanced protein synthesis of the cells, on the basis of data obtained from in-vitro experiments with cell free systems, is to be attributed mainly to the increased content of translation factors in the cytosol.