Multifunctional protein involved in the transcription and replication of viral RNAs. Contains the proteinases responsible for the cleavages of the polyprotein. May play a role in the modulation of host cell survival signaling pathway by interacting with host PHB and PHB2 (By similarity). Indeed, these two proteins play a role in maintaining the functional integrity of the mitochondria and protecting cells from various stresses (By similarity). Responsible for the cleavages located at the N-terminus of the replicase polyprotein (By similarity). In addition, PL-PRO possesses a deubiquitinating/deISGylating activity and processes both 'Lys-48'- and 'Lys-63'-linked polyubiquitin chains from cellular substrates (By similarity). Plays a role in host membrane rearrangement that leads to creation of cytoplasmic double-membrane vesicles (DMV) necessary for viral replication (By similarity). Alone is able to induce paired membranes (By similarity). Coexpression of nsp3 and nsp4 does not result in the formation of DMVs (By similarity). Responsible for the majority of cleavages as it cleaves the C-terminus of replicase polyprotein at 11 sites. Recognizes substrates containing the core sequence [ILMVF]-Q-|-[SGACN]. Inhibited by the substrate-analog Cbz-Val-Asn-Ser-Thr-Leu-Gln-CMK. Forms a hexadecamer with nsp8 (8 subunits of each) that may participate in viral replication by acting as a primase. Alternatively, may synthesize substantially longer products than oligonucleotide primers. Forms a hexadecamer with nsp7 (8 subunits of each) that may participate in viral replication by acting as a primase. Alternatively, may synthesize substantially longer products than oligonucleotide primers. Plays an essential role in viral replication by forming a homodimer that binds single-stranded RNA. Plays a pivotal role in viral transcription by stimulating both nsp14 3'-5' exoribonuclease and nsp16 2'-O-methyltransferase activities (By similarity). Therefore plays an essential role in viral mRNAs cap methylation (By similarity). Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Interacts with host PHB and PHB2. Interacts with papain-like protease and non-structural protein 6. Monomer. Homodimer. Only the homodimer shows catalytic activity. Eight copies of nsp7 and eight copies of nsp8 assemble to form a heterohexadecamer dsRNA-encircling ring structure. Eight copies of nsp7 and eight copies of nsp8 assemble to form a heterohexadecamer dsRNA-encircling ring structure (By similarity). Interacts with ORF6 protein (By similarity). Homodimer. Homododecamer. Gammacoronaviruses induce membrane zippering to form zippered endoplasmic reticulum (zER). Localizes in virally-induced cytoplasmic double-membrane vesicles (By similarity). Gammacoronaviruses induce membrane zippering to form zippered endoplasmic reticulum (zER) (By similarity). Gammacoronaviruses induce membrane zippering to form zippered endoplasmic reticulum (zER). nsp7, nsp8, nsp9 and nsp10 are localized in cytoplasmic foci, largely perinuclear. Late in infection, they merge into confluent complexes. nsp7, nsp8, nsp9 and nsp10 are localized in cytoplasmic foci, largely perinuclear. Late in infection, they merge into confluent complexes. nsp7, nsp8, nsp9 and nsp10 are localized in cytoplasmic foci, largely perinuclear. Late in infection, they merge into confluent complexes. nsp7, nsp8, nsp9 and nsp10 are localized in cytoplasmic foci, largely perinuclear. Late in infection, they merge into confluent complexes. Isoform Replicase polyprotein 1ab is produced by -1 ribosomal frameshifting at the 1a-1b genes boundary. Isoform Replicase polyprotein 1a is produced by conventional translation. The hydrophobic region HD1 probably mediates the membrane association of the replication complex. The hydrophobic region HD2 probably mediates the membrane association of the replication complex. The hydrophobic region HD3 probably mediates the membrane association of the replication complex. Specific enzymatic cleavages in vivo by its own proteases yield mature proteins (By similarity). 3C-like proteinase nsp5 liberates nsps 6-16 from the polyprotein (By similarity). Papain-like and 3C-like proteinases are autocatalytically processed. N-glycosylated. Belongs to the coronaviruses polyprotein 1ab family.