Sequence determination of the 3' terminal T1 oligonucleotide of 18S ribosomal RNA.

We have reexamined the primary structure of the 3' terminal oligonucleotide of 18S RNA from chicken fibroblasts and have shown, contrary to previously published results that this extremity G-A-U-C-A-U-U-AOH is identical to that of the rabbit, drosophila and bombyx. Furthermore the electrophoretic mobility and composition of the 3' terminal oligonucleotides of 18S RNA from rat and human cells are similar to that of other RNAs and show that the identity of structure for this region of 18S RNA extends to include all tested species between yeast and man. This finding reveals a marked degree of evolutionary constraint on the structure of this region.