Behaviour of turnip yellow mosaic virus nucleoproteins under alkaline conditions

A modified CsCl density gradient procedure is described by which purified preparations of turnip yellow mosaic virus (TYMV) can be fractionated to give 12 nucleoprotein components. When the B1 nucleoprotein is subjected to pH 11.5-11.6 in 1 M KCl (conditions under which artificial empty protein shells are formed), the apparent radius (r) of the virus increases from about 14.6 to 15.2 nm within 30 sec. The increase in r is most probably due to swelling of the particles. Escape of the RNA from these particles is completed in 3-10 min, while RNA degradation continues for at least 30 min. On return to pH 7.0, r returns to about 14.6 nm. When any of the minor nucleoprotein fractions containing less than the full complement of RNA are subjected to the above conditions, the RNA does not escape from the particle. Experiments with the B0 components also showed that these particles did not give an increase in r, although the RNA was degraded to about the same extent as that of the B1 nucleoprotein.