In vitro incorporation of amino acids into the proteins of isolated nuclear ribosomes

Abstract

Ribonucleoprotein particles of diverse composition and metabolic activity can be extracted from the isolated thymus cell nucleus. If properly supplemented these ribosomes remain capable of active amino acid incorporation into their constituent proteins. This process requires adenosine triphosphate, amino acid activating enzymes, and guanosine triphosphate. Thymus nuclear ribosomes are irreversibly inactivated by brief exposure to hypertonic sucrose solutions, either before or after extraction from the nucleus. While in the nucleus they are resistant to ribonuclease digestion, but after their isolation, ribonuclease attacks the particles and destroys their activity. The addition of deoxyribonucleic acid of diverse sources stimulates amino acid incorporation by isolated nuclear ribosomes, but other polyanions may be inhibitory. This role of deoxyribonucleic acid and the influence of position within the cell nucleus upon the metabolism of nuclear ribosomes is discussed.