The larger ribosomal subunit from all organisms examined to date has been found to contain one RNA molecule with a molecular weight of 40, 000, the socalled "5S RNA". The primary structures of 5S RNAs from more than ten species have been determined so far. A large number of models for their secondary structure have been proposed on the basis of many experimental and theoretical studies. However, little is known about the real function of 5S RNA in ribosome structure at the presnet time.
In this article, recent studies on primary and secondary structure of 5S RNA are briefly reviewed and several secondary structure models, including ours, are compared with each other. Some of the possible functions of 5S RNA expected from our secondary structure model are also discussed.
