The different products prevent the establishment of cellular antiviral state by blocking the interferon-alpha/beta (IFN-alpha/beta) and IFN-gamma signaling pathways. They inhibit IFN-alpha/beta induced tyrosine phosphorylation of STAT1 and STAT2. Blocking the IFN-alpha/beta pathway requires binding to STAT1 in the cytoplasm. They inhibit IFN-gamma induced serine phosphorylation of STAT1. Block the IFN-gamma pathway by binding to and stabilizing the parallel form of the STAT1 dimer, further inducing high-molecular-weight complex formation and inhibition of transcription by IFN-gamma. May also have a role in preventing the cell to enter apoptosis. Modulate regulation of viral transcription and replication. Overexpression inhibits the viral RNA polymerase. The absence of all C', C and Y1 proteins leads to viral delayed growth. Plays an important role in virion particles release. Modulates virion shape. The different isoforms interact (via C-terminus) with unphosphorylated and phosphorylated human STAT1 (via N-terminus), favoring the formation of parallel STAT1 homodimers. The different isoforms do not interact with host STAT2. C protein interacts with L protein; this interaction has an inhibitory effect on viral transcription and replication. Protein C' seems to localize around the Golgi. The disordered region at the N-terminus is involved in C protein self-degradation in trans. This self-degradation of C protein may play a role in the regulation of viral RNA synthesis. The disordered region at the N-terminus is also involved in the host STAT1 degradation in order to counteract the host innate antiviral response. Protein Y1 is produced not only by alternative initiation, but also by proteolytic cleavage of C'. Only alternative initiation is detected in vitro, whereas in vivo cleavage seems to be predominant. The C protein is found in virion at a ratio of approximately 40 molecules per virion, presumably associated with the nucleocapsid. The P/V/C gene has two overlapping open reading frames. One encodes the P/V/W proteins and the other the C/Y proteins. The initiator methionine is coded by an unusual start codon ACG. Most abundant isoform in infected cells. Belongs to the respirovirus protein C family. The C' protein uses an unusual ACG start codon.