Plays a major role in antagonizing the type I IFN-mediated antiviral response by degrading or inhibiting multiple cellular factors required for either IFN induction or response pathways. Acts cooperatively with NS2 to repress activation and nuclear translocation of host IFN-regulatory factor IRF3. Also disrupts the association of IRF3 with CREBBP. Interacts with host mitochondrial-associated membrane (MAM) MAVS and prevents the interaction with DDX58/RIG-I. Interacts with TRIM25 to suppress TRIM25-mediated DDX58 ubiquitination and thereby DDX58-MAVS interaction. Together with NS2, participates in the proteasomal degradation of host STAT2, IRF3, IRF7, TBK1 and DDX58/RIG-I through a NS-degradasome involving CUL2 and Elongin-C. The degradasome requires an intact mitochondrial MAVS. Decreases the levels of host TRAF3 and IKBKE/IKK-epsilon. As functions other than disruptions of the type I IFN-mediated antiviral signaling pathways, induces host SOCS1 and SOCS3 expression. Suppresses premature apoptosis by an NF-kappa-B-dependent, interferon-independent mechanism and thus facilitates virus growth. Additionally, NS1 may serve some inhibitory role in viral transcription and RNA replication. Suppresses proliferation and activation of host CD103+ CD8+ cytotoxic T-lymphocytes and Th17 helper T-lymphocytes. Monomer. Homomultimer. Heteromultimer with NS2. Interacts with the matrix protein M. Interacts with host ELOC and CUL2; this interaction allows NS1 to form an active E3 ligase with ELOC and CUL2. Interacts with host IRF3; this interaction leads to the disrupted association of IRF3 with CREBBP and thus reduced binding of IRF3 to the IFN-beta promoter. Interacts with host MAVS; this interaction prevents MAVS binding to DDX58 and inhibits signaling pathway leading to interferon production. Interacts with host MAP1B/microtubule-associated protein 1B. Interacts with host TRIM25 (via SPRY domain); this interaction suppresses DDX58 ubiquitination and results in decreased interaction between DDX58 and MAVS. Most NS1 resides in the mitochondria as a heteromer with NS2. N-terminus is important for IKBKE/IKK-epsilon reduction. The DNLP motif has IFN suppressive functions like binding to host MAP1B. Belongs to the pneumovirus non-structural protein 1 family.