Hsp72 recognizes a P binding motif in the measles virus N protein C-terminus

The major inducible 70-kDa heat shock protein (hsp72) binds measles virus (MV) nucleocapsids and increases MV gene expression. The cytoplasmic tail of the MV N protein (NTAIL) contains three hydrophobic domains (Box-1-3) that are potential targets of hsp72 interaction. Low affinity binding to Box-3 is correlated to hsp72-dependent stimulation of MV minireplicon reporter gene expression whereas interactions between hsp72 and Box-1 and/or -2 have not been documented. The present work showed that virus deficient in Box-3/hsp72 interaction retains the ability to form nucleocapsid/hsp72 complexes, identifying Box-2 but not Box-1 as a mediator of high affinity hsp72 binding. Box-2 is the binding site for the viral P protein X domain (XD), where P tethers the viral polymerase to nucleocapsid in support of transcription and genome replication, and competitive inhibition of XD binding to NTAIL by hsp72 was shown. Recognition of a common binding site by P and hsp72 represents a potential mechanism for host cell modulation of viral gene expression.