Ribosomes from Xenopus laevis ovaries and the polyuridylic acid-directed biosynthesis of polyphenylalanine

Abstract
Single ribosomes account for 90% or more of the ribosome fraction of Xenopus laevis ovaries. These ribosomes have low endogenous activity in a cell-free protein-synthesizing system but synthesize polyphenylalanine in the presence of poly U under conditions comparable with those reported for mammalian or bacterial systems. These observations agree with the view that the ribosome is deficient in mRNA.