A temperature-sensitive mutant of Newcastle disease virus which is affected in both haemagglutinin-neuraminidase and matrix proteins.

Virions prepared from a non-revertible temperature-sensitive (ts) mutant (ts53) of Newcastle disease virus (NDV) grown in ovo at the permissive temperature (34 degrees C) possessed thermolabile haemagglutination and neuraminidase activities compared with parental (ts+) virions. Purified haemagglutinin-neuraminidase (HN) protein from ts53 virions was also more thermolabile than ts+ HN protein. SDS-PAGE analysis of [3H]leucine pulse- and pulse/chase-labelled NDV proteins synthesized in chick embryo fibroblasts following infection with ts+ and ts53 virus revealed that ts53 matrix (M) protein was unstable and disappeared during chase incubations only at the non-permissive temperature (42 degrees C). The non-revertibility of the ts53 mutant may indicate that it is a double mutant affected in both HN and M genes; alternatively this mutant may only be affected in the HN gene, the close physical association of the thermolabile HN with the M protein during virus maturation resulting in the lack of protection of the M protein from the action of cellular proteases at the non-permissive temperature.