Abstract
A 5-helix secondary structural model is proposed for eukaryotic cytoplasmic 5S rRNA. All available sequence data are consistent with this model including those from Chlorella 5S rRNA in which sequence is revised. Various architectural features of eukaryotic 5S rRNA are summarized in terms of this secondary structural model. Previous failures to identify universal models for 5S rRNA secondary structure stem from significant differences in architecture between eukaryotic cytoplasmic and eubacterial 5S rRNA. The usual 4-helix model for eubacterial 5S rRNA secondary structure nevertheless shares several structural features with the 5-helix model presented here for cytoplasmic 5S rRNA. These 2 classes of 5S rRNA are probably the result of evolutionary divergence rather than convergence.