Temperature-sensitive mutant of Newcastle disease virus which has an altered nucleocapsid-associated protein

Analysis of six temperature-sensitive (ts) mutants of Newcastle disease virus (NDV) representing each of six complementation groups by both SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional gel electrophoresis revealed that in only one mutant was there an alteration in the isoelectric point of a protein. This altered protein was the nucleocapsid-associated protein, NAP. In addition, the mobility of the haemagglutinin-neuraminidase protein, HN, was decreased on non-reduced SDS-PAGE in this mutant. All independent ts+ clones derived from this mutant had normal NAP but HN protein migrated at the decreased rate. Haemagglutinating activity of wide-type (ts+) and ts virions was equally thermostable. Wild-type and ts+ clones derived from this ts mutant were RNA(+) at both permissive and non-permissive temperatures, whereas the ts mutant was RNA(-) at the non-permissive temperature. This ts mutant appears to be a double mutant in both HN and NAP genes, the latter only being a temperature-sensitive lesion which affects virus-directed RNA synthesis.