Localization of 2',3'-decycling phosphodiesterases in the Newcastle disease virus virion

Purified Newcastle disease virus (NDV) virions possess 2',3'-cyclic nucleotide 2'-phosphohydrolase (2'-CNPase) and 2',3'-cyclic nucleotide 3'-phosphohydrolase (3'-CNPase) activities. These enzyme activities cannot be removed from the virion even after extensive purification by chromatography on controlled-pore glass. In the intact virion, the 3'-CNPase activity was stimulated by Triton X-100, while the 2'-CNPase activity was partially inhibited. We have prepared the NDV subunits and have shown that 3'-CNPase was associated exclusively with the viral nucleocapsid. In contrast, the 2'-CNPase activity was associated with both the envelope as well as the nucleocapsid. A threshold amount of both enzyme activities was detected in viral M protein.