ID   X_WHV1                  Reviewed;         141 AA.
AC   P03167;
DT   21-JUL-1986, integrated into UniProtKB/Swiss-Prot.
DT   21-JUL-1986, sequence version 1.
DT   23-FEB-2022, entry version 80.
DE   RecName: Full=Protein X {ECO:0000255|HAMAP-Rule:MF_04074};
DE   AltName: Full=HBx {ECO:0000255|HAMAP-Rule:MF_04074};
DE   AltName: Full=Peptide X {ECO:0000255|HAMAP-Rule:MF_04074};
DE   AltName: Full=pX {ECO:0000255|HAMAP-Rule:MF_04074};
GN   Name=X {ECO:0000255|HAMAP-Rule:MF_04074};
OS   Woodchuck hepatitis B virus (isolate 1) (WHV).
OC   Viruses; Riboviria; Pararnavirae; Artverviricota; Revtraviricetes;
OC   Blubervirales; Hepadnaviridae; Orthohepadnavirus.
OX   NCBI_TaxID=10430;
OH   NCBI_TaxID=9995; Marmota monax (Woodchuck).
RN   [1]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RX   PubMed=7086958; DOI=10.1128/jvi.41.1.51-65.1982;
RA   Galibert F., Chen T.N., Mandart E.;
RT   "Nucleotide sequence of a cloned woodchuck hepatitis virus genome:
RT   comparison with the hepatitis B virus sequence.";
RL   J. Virol. 41:51-65(1982).
CC   -!- FUNCTION: Multifunctional protein that plays a role in silencing host
CC       antiviral defenses and promoting viral transcription. Does not seem to
CC       be essential for HBV infection. May be directly involved in development
CC       of cirrhosis and liver cancer (hepatocellular carcinoma). Most of
CC       cytosolic activities involve modulation of cytosolic calcium. The
CC       effect on apoptosis is controversial depending on the cell types in
CC       which the studies have been conducted. May induce apoptosis by
CC       localizing in mitochondria and causing loss of mitochondrial membrane
CC       potential. May also modulate apoptosis by binding host CFLAR, a key
CC       regulator of the death-inducing signaling complex (DISC). Promotes
CC       viral transcription by using the host E3 ubiquitin ligase DDB1 to
CC       target the SMC5-SMC6 complex to proteasomal degradation. This host
CC       complex would otherwise bind to viral episomal DNA, and prevents its
CC       transcription. Moderately stimulates transcription of many different
CC       viral and cellular transcription elements. Promoters and enhancers
CC       stimulated by HBx contain DNA binding sites for NF-kappa-B, AP-1, AP-2,
CC       c-EBP, ATF/CREB, or the calcium-activated factor NF-AT.
CC       {ECO:0000255|HAMAP-Rule:MF_04074}.
CC   -!- SUBUNIT: May form homodimer. May interact with host CEBPA, CFLAR,
CC       CREB1, DDB1, E4F1, HBXIP, HSPD1/HSP60, NFKBIA, POLR2E and SMAD4.
CC       Interacts with host SMC5-SMC6 complex and induces its degradation.
CC       {ECO:0000255|HAMAP-Rule:MF_04074}.
CC   -!- SUBCELLULAR LOCATION: Host cytoplasm {ECO:0000255|HAMAP-Rule:MF_04074}.
CC       Host nucleus {ECO:0000255|HAMAP-Rule:MF_04074}. Host mitochondrion
CC       {ECO:0000255|HAMAP-Rule:MF_04074}. Note=Mainly cytoplasmic as only a
CC       fraction is detected in the nucleus. In cytoplasm, a minor fraction
CC       associates with mitochondria or proteasomes. {ECO:0000255|HAMAP-
CC       Rule:MF_04074}.
CC   -!- PTM: A fraction may be phosphorylated in insect cells and HepG2 cells,
CC       a human hepatoblastoma cell line. Phosphorylated in vitro by host
CC       protein kinase C or mitogen-activated protein kinase. N-acetylated in
CC       insect cells. {ECO:0000255|HAMAP-Rule:MF_04074}.
CC   -!- SIMILARITY: Belongs to the orthohepadnavirus protein X family.
CC       {ECO:0000255|HAMAP-Rule:MF_04074}.
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DR   EMBL; J02442; -; NOT_ANNOTATED_CDS; Genomic_DNA.
DR   PIR; A03720; QQVLC1.
DR   PDB; 3I7K; X-ray; 2.80 A; B=86-99.
DR   PDBsum; 3I7K; -.
DR   SMR; P03167; -.
DR   EvolutionaryTrace; P03167; -.
DR   Proteomes; UP000007631; Genome.
DR   GO; GO:0033650; C:host cell mitochondrion; IEA:UniProtKB-SubCell.
DR   GO; GO:0042025; C:host cell nucleus; IEA:UniProtKB-SubCell.
DR   GO; GO:0039652; P:induction by virus of host NF-kappaB cascade; IEA:UniProtKB-UniRule.
DR   GO; GO:0039592; P:suppression by virus of G2/M transition of host mitotic cell cycle; IEA:UniProtKB-UniRule.
DR   GO; GO:0006351; P:transcription, DNA-templated; IEA:UniProtKB-UniRule.
DR   GO; GO:0019079; P:viral genome replication; IEA:UniProtKB-UniRule.
DR   HAMAP; MF_04074; HBV_X; 1.
DR   InterPro; IPR000236; Transactivation_prot_X.
DR   Pfam; PF00739; X; 1.
PE   1: Evidence at protein level;
KW   3D-structure; Activation of host NF-kappa-B by virus; Activator; Apoptosis;
KW   Host cytoplasm; Host G2/M cell cycle arrest by virus; Host mitochondrion;
KW   Host nucleus; Host-virus interaction;
KW   Modulation of host cell cycle by virus; Transcription;
KW   Transcription regulation.
FT   CHAIN           1..141
FT                   /note="Protein X"
FT                   /id="PRO_0000222370"
FT   REGION          24..51
FT                   /note="Disordered"
FT                   /evidence="ECO:0000256|SAM:MobiDB-lite"
FT   REGION          68..113
FT                   /note="Mitochondrial targeting sequence"
FT                   /evidence="ECO:0000255|HAMAP-Rule:MF_04074"
FT   HELIX           87..96
FT                   /evidence="ECO:0007829|PDB:3I7K"
SQ   SEQUENCE   141 AA;  15222 MW;  4728019844561D85 CRC64;
     MAARLCCQLD PARDVLLLRP FGSQSSGPPF PRPSAGSAAS PASSLSASDE SDLPLGRLPA
     CFASASGPCC LVVTCAELRT MDSTVNFVSW HANRQLGMPS KDLWTPYIRD QLLTKWEEGS
     IDPRLSIFVL GGCRHKCMRL P