Ribosomes from aging mice are not generally deficient in cell-free protein synthesis

Cell-free protein synthesis by mouse liver ribosomes was examined as a function of the age of individual ribosome donors. In two strains of mouse, one long-lived and one short-lived, both the fraction of polyribosomes and the rate of in vitro ribosomal protein synthesis remained essentially constant throughout the lifespan, although in each "old" group one of three mice fell below the range of values observed for all other mice. Poly(U) stimulation of preincubated ribosome preparations similarly did not change with senescence; whereas poly(U)-directed synthesis by washed monosomes, pelleted after messenger run-off, increased two-fold for old mice. These results indicate that ribosomes of old mice are not necessarily defective in protein-synthesizing capacity, as previously reported, but may become defective in particular individuals.