Irregularities in the circular dichroism of oligoribonucleotides.

Marked anomalies, previously unresolved, exist in the CD spectra of oligoadenylates and oligouridylates at the pentamer or tetramer stage, indicating that these molecules differ in conformation from the preceding and the following member of the series. The CD of oligoadenylates retains a positive Cotton effect even at 80 degrees C. Caution must be exerted when predicting oligonucleotide structures from CD spectra.