An RNA core in the 30S ribosomal subunit of Escherichia coli and its structural and functional significance.

1. Evidence is presented for the occurrence of a very stable RNA core (S4-RNA) in "native" 16S RNA that is also present in the 30S subunit of Escherichia coli. A model giving the approximate location of this RNA core in the 30S subunit is presented. 2. It is proposed (a) that this S4-RNA acts as a nucleus for the assembly of the 30S subunit, and (b) that a small class of "linkage" proteins, including S4, further facilitate the assembly of the proteins to the RNA, thereby explaining some of the "cooperative" effects that are observed during in vitro assembly. 3. Evidence for the importance of the RNA core in the functioning of the ribosome is discussed.