Study of Several Factors in RNA-protein Cross-link Formation Induced by Ionizing Radiations Within 70S Ribosomes of E. Coli MRE 600

Summary

The induction of RNA-protein crosslinks in E. coli 70S ribosomes by γ-irradiation was studied by measuring the dependence of cross-link formation on ribosome concentration. The inverse dependence of cross-link percentage upon concentration up to at least 20 A_260nm units ml⁻¹ indicate that indirect effects seem to play a more major part than direct effects for these ribosome concentrations. The effect of various gases and free radical scavengers was used to determine the roles of the radicals H·, CO⁻₂·, OH· and e⁻_aq and to estimate their relative efficiencies for cross-links. They were found to be: 7·2(H·), 6(CO⁻₂·), 2(OH·) and 1(e⁻_aq). The extent of RNA–protein cross-link production in 70S ribosomes induced by γ-rays and neutrons in the presence and absence of oxygen was also investigated. Cross-link formation was estimated by separation of linked and unlinked material on nitrocellulose filters or after separation by SDS-sucrose gradient centrifugation under dissociating conditions. Oxygen inhibited cross-link formation by both neutrons and γ-rays. However, very few cross-links were formed in de-aerated solutions by exposure to neutrons, compared to those produced by γ-rays under the same conditions. This suggests that molecular oxygen generated along the secondary particle track can reduce the formation of RNA–protein cross-links.

• ribosomes
• RNA–protein cross-links
• γ-rays
• radical scavengers
• neutrons