Studies on a measles virus variant inducing persistent infections in cultured cells.I. Isolation and characterization of plaque purified virus clones.

Attempts were made to characterized by a plaque assay two variants of the Edmonston strain of measles virus and to obtain plaque purified virus populations. The UP non-cytocidal variant, in all the examined cell systems, mainly produced small but also large plaques; the DP cytocidal variant always large plaques. Three clones, UP-SP4, UP-LP4 and DP-LP4, were derived by plaque purfication respectively of the UP small plaque, UP large plaque and DP large plaque forming particles. The virus populations of the clones could be distinguished by some other biological and physical characters: cytopathic effect in roller tube cultures, growth potential in HeLa cells, thermal stability at 45 degrees C, stability of the properties during serial passages at different input multiplicity. The hypothesis was supported that the typical properties of the UP and DP variants are host-independent and genetically controlled viral markers.