Effects of X-Irradiation on RNA and Protein Synthesis in HeLa Cells

Abstract

Alterations in protein and RNA metabolism in asynchronously growing HeLa cell population following 2000 rads of x-irradiation were studied using sucrose density gradients, radioactive precursor labeling, and autoradiographic procedures. It was found that irradiation reduced protein synthesis within a 2-hour period while a depression of RNA synthesis by x-irradiation was evident somewhat later. Rapidly labeled ribosome precursor RNA was delayed in its transformation into smaller RNA molecules as revealed by pulse chase experiments at a time when inhibition of total RNA synthesis becomes noticeable after 2000 rads of x-irradiation. Specific activities of polysomal fractions from irradiated and control cells labeled with radioactive amino acids are almost identical, but the total amount of radioactivity was less in the sedimentation profile of irradiated cells than in controls. Several possible mechanisms that could result in the depression of protein synthesis are discussed.