Concluding Remarks

Abstract

The first session of the meeting focused on ribosome structure. The data presented in this session emphasized once again that contrary to the previously prevailing view the ribosomal RNA may fulfill active roles in different ribosomal functions and is more than a framework to which ribosomal proteins are attached. Thus, information obtained from structural work on the ribosomal RNA is apt to provide further, if not ultimate, insight into the ribosomal mechanisms of protein synthesis. Cantor summarized the results obtained by the electron microscopic analysis of long distance psoralen cross-links on E. coli 16S RNA with established orientation. From the estimated distances of the beginning and end of the cross-linked loop from the 5′ end plotted as points in a triangular field, a pattern starts to emerge now, in general confirmatory, of the secondary structure models proposed for the 16S RNA. Additional cross-links observed by this approach, but thus far not considered in the secondary structure models are suggestive of the contacts determining the tertiary structure of the RNA molecule. The diversity of the contacts made by the 3′end of 16S RNA deserves here particular attention since it may attest to structural rearrangements of the 3′ end in different steps of protein synthesis. The identification of the sequences involved in the cross-links is desirable for the test of secondary structure models and the construction of three-dimensional models. Cantor described a strategy to determine such sequences based on the hybridization of the RNA samples enriched by electrophoresis in particular cross-links to appropriate endlabeled complementary DNA fragments and subsequent exposure of the RNA-DNA hybrid to single-strand specific mung bean nuclease digestion.