Study of the circular dichroism of bacteriophage phi 6 and phi 6 nucleocapsid

We have studied the CD of both bacteriophage ?6 and ?6 nucleocapsid in order to assess the in situ state of the viral, double-stranded RNA (dsRNA). The results showed that packaged ?6 RNA is slightly hyperdichroic (4–5%) at 264 nm relative to dsRNA in solution. Also, the CD of dsRNA within both the virus and the nucleocapsid was unlike CD spectra of any of the three types of dsRNA condensed in vitro, as described in the accompanying paper. Using a curve-fitting program described elsewhere (Edmondson, S.P. & Gray, D.M. (1983) Nucleic Acids Res. 11 , 175–192), we have fit reference CD spectra of ?6 RNA and protein to measured CD spectra of ?6 intact phage and nucleocapsid. Results of the computer analysis indicated that ?6 RNA in situ is spectrally similar to dsRNA that is slightly dehydrated.