Studies on hypophyseal isografts in mice. II. Properties of polyribosomes

Polyribosomes, characterized by sedimentation behavior and electron microscopy, have been prepared from hypophyseal isografts in kidney. These preparations have incorporation ability for amino acids in vitro and can be stimulated for phenylalanine incorporation by polyuridylic acid, similar to the rat liver system. The 100,000 × g supernatant fraction contains a factor which protects the integrity of polyribosomes during incubation at 37°C.