CONFORMATIONS OF SINGLE-STRANDED DNA AND COAT PROTEIN IN FD BACTERIOPHAGE AS REVEALED BY ULTRAVIOLET ABSORPTION SPECTROSCOPY

The single-stranded DNA in the virion has a molar extinction coefficient per phosphate group at 260 mμ of 6750 ± 300. This low value suggests that the DNA is in a base-stacked conformation. Hypochromism, in the 190 to 205 mμ range, of the protein subunits in the virion indicates an α-helix content of 80 to 90%. According to criteria for distinguishing the effects of spectral shifts and changes in absorption intensity on difference spectra, the spectrum for intact phage shows significant hyperchromicity centered around 290 mμ relative to the spectra of separated DNA and protein. © 1969.