Abstract
With the demonstration of the existence of a heavy protein in plant tissues diseased with tobacco mosaic virus 1 it became inevitable that similar proteins should be sought in other kinds of virus-infected tissues. Most viruses are more or less unstable towards the chemicals which would naturally be used in efforts to concentrate and purify them. The air-ultracentrifuge 2 has, however, furnished a new tool 3 which has been successful in extracting and purifying several of the less stable virus proteins causing plant diseases 4 and in preparing a similar substance 5 from virus-induced rabbit papillomas (Shope). The same type of ultracentrifugal examination has now been made of tissues diseased with the virus of equine encephalomyelitis.∗
As in the previous ultracentrifugal concentrations an angle-centrifuged tissue suspension was ultracentrifuged for one to one and a half hours in a maximum field of ca 50,000 times gravity. All but a trace of the virus activity was thus sedimented. The translucent pellet formed at the bottom of the tube by this ultracentrifugation was resuspended in a suitable solvent and the aggregated colloidal matter thrown down by another low speed centrifugation. Ultracentrifugation of this solution furnished a smaller but cleaner pellet. On occasion the purification of this pellet was carried further by a repetition of the cycle of centrifugation, ultracentrifugation and resuspension. The virus of equine encephalomyelitis is not thermostable; it rapidly becomes non-infectious at room temperature and cannot be relied upon to preserve its activity for long periods of time in the icebox. Therefore all manipulations, including the ultra-centrifugations, were carried out without delay and in the cold.
Both the original suspensions and those resulting from the ultra-centrifugations were examined with an analytical ultracentrifuge arranged for photography according to the classical absorption method of Svedberg.
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