Preparation and Properties of Cucumber Virus 4

A substantial relationship between cucumber viruses 3 and 4 and certain members of the tobacco mosaic virus group may be demonstrated by a comparison of their physicochemical properties and by serological tests (l-3). However, the test which would establish conclusively kinship between these nucleoproteins, namely the immunization of a plant diseased with cucumber virus 3 or 4 against infection from a strain of tobacco mosaic virus or the reverse, has been entirely lacking, for no host common to the two groups of viruses has thus far been found (1, 2, 4). A comparative study of cucumber viruses 3 and 4 and strains of tobacco mosaic virus has been undertaken in an effort to find a chemical explanation for the similarities and differences existing between these related nucleoproteins. Moreover, a study of the cucumber viruses is of unique interest in connection with the relationship between host and infectious agent, for, contrary to the usual case with plant viruses, cu&mber viruses 3 and 4 have been found transmissible in but one family of plants (4). Earlier experiments with purified preparations of cucumber viruses 3 and 4 have been comparatively limited, and the data presented have dealt chiefly with cucumber virus 3 (2, 5, 6). Further, in most of these investigations chemical methods for purification were employed. It is known now t,hat such methods may yield preparations which contain variable amounts of altered virus and show proportionally less activity than preparations obtained by physical means alone (7-10). A description of the isolation and purification of cucumber virus 4 by physical methods and of the properties of the purified virus is given in t’he present paper.