Plays an essential role in the inhibition of host apoptosis. Mediates host mitochondria-mediated apoptosis through interaction with the mitochondrial antiviral signaling protein/MAVS and thereby promotes viral persistence in host central nervous system. Within the host nucleus, regulates viral RNA synthesis and polymerase complex assembly. Interacts with P and N proteins. These interactions presumably promote nuclear targeting of the X protein in infected cells (PubMed:10708460). Interacts with host MAVS; this interaction inhibits MAVS-induced apoptosis (PubMed:23702035). Phosphorylated. The P/X gene has 2 overlapping open reading frames. One encodes the P protein and the other the X protein. The p24, X and p16 proteins are produced by ribosomal leaky scanning.