Die rol van ribosomale RNA in die struktuur en funksie van ribosome
Pretorius, Petrus Jacobus
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The relationship of the structure and function of the ribosomes of E. coli was investigated. This was done by determining the effect of ionisation radiation on the function and physical properties of the ribosomes . Ribosomes were isolated from an E. CQli cell- free extract and exposed to gamma- rays. The effect of the radiation was evaluated by determining the ability of the irradiated ribosomes to promote polypeptide synthesis . An exponential decline of the activity with radiation time was observed. The effect of ionisation radiation on the sedimentation properties of the ribosomes was determined by means of density gradiant centrifugation. The radiation of the ribosomes resulted in a change of the 70S- ribosome to a intermediate component between 70S and SOS. The original 705-ribosome was restored by means of dialysis. It was shown that the free 70S-ribosome is involved in this change in the sedimentation pattern. The ribosomal RNA was fragmented at random by the radiation into pieces of variable size. These ruptures were not restored by dialysis of the irradiated ribosomes. It seems that the overall ·structure of the ribosome is not disorganised in spite of its fragmented RNA. The origin and nature of this intermediate "70S"-ribosome and the significance of the fragmented RNA in maintaining the structure of the ribosome is discussed. The most probable origin of this intermediate "70S"-ribosome is a dissociation-reassociation equilibrium system with a intermediate sedimentation value between 705 en 505.