ID   ST_POVBK                Reviewed;         172 AA.
AC   P03082;
DT   21-JUL-1986, integrated into UniProtKB/Swiss-Prot.
DT   21-JUL-1986, sequence version 1.
DT   02-SEP-2026, entry version 112.
DE   RecName: Full=Small t antigen;
DE            Short=ST;
DE            Short=ST-AG;
OS   BK polyomavirus (BKPyV) (Human polyomavirus 1).
OC   Viruses; Floreoviria; Shotokuvirae; Cossaviricota; Papovaviricetes;
OC   Sepolyvirales; Polyomaviridae; Betapolyomavirus.
OX   NCBI_TaxID=1891762;
OH   NCBI_TaxID=9606; Homo sapiens (Human).
RN   [1]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RC   STRAIN=Dunlop;
RX   PubMed=229976; DOI=10.1016/0092-8674(79)90209-5;
RA   Seif I., Khoury G., Dhar R.;
RT   "The genome of human papovavirus BKV.";
RL   Cell 18:963-977(1979).
RN   [2]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RC   STRAIN=MM;
RX   PubMed=228391; DOI=10.1126/science.228391;
RA   Yang R.C.A., Wu R.;
RT   "BK virus DNA: complete nucleotide sequence of a human tumor virus.";
RL   Science 206:456-462(1979).
RN   [3]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RC   STRAIN=MM;
RX   PubMed=6246273; DOI=10.1128/jvi.34.2.416-430.1980;
RA   Yang R.C.A., Young A., Wu R.;
RT   "BK virus DNA sequence coding for the t and T antigens and evaluation of
RT   methods for determining sequence homology.";
RL   J. Virol. 34:416-430(1980).
RN   [4]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RC   STRAIN=MM;
RX   PubMed=228246; DOI=10.1093/nar/7.3.651;
RA   Yang R.C.A., Wu R.;
RT   "Comparative study of papovavirus DNA: BKV(MM), BKV(WT) and SV40.";
RL   Nucleic Acids Res. 7:651-668(1979).
CC   -!- FUNCTION: Promotes efficient viral genome replication by accelerating
CC       both G1 and S phase progression of the cell cycle. Inhibits host PP2A
CC       by binding to the A subunit, thereby displacing lower affinity
CC       regulatory B subunit. Inactivation of PP2A in turn results in the
CC       transactivation of cyclin A and cyclin D1 promoters. Late during the
CC       infection cycle, ST may induce dephosphorylation of host MTOR, leading
CC       to the inhibition of cap-dependent translation. May establish and
CC       maintain high levels of viral genomes during persistent infection in
CC       cell culture. {ECO:0000250|UniProtKB:P03081}.
CC   -!- SUBUNIT: Interacts with host PPP2R1A; the interaction inhibits PP2A
CC       activity. {ECO:0000250|UniProtKB:P03081}.
CC   -!- SUBCELLULAR LOCATION: Host cytoplasm. Host nucleus
CC       {ECO:0000250|UniProtKB:P03081}.
CC   -!- ALTERNATIVE PRODUCTS:
CC       Event=Alternative splicing; Named isoforms=2;
CC       Name=Small t antigen;
CC         IsoId=P03082-1; Sequence=Displayed;
CC       Name=Large T antigen;
CC         IsoId=P03071-1; Sequence=External;
CC   -!- DOMAIN: The common region of ST and LT proteins comprises the J domain.
CC       This domain is essential for multiple viral activities, including
CC       virion assembly, viral DNA replication, transformation and
CC       transcriptional activation. This domain is also required for cyclin A-
CC       transactivating activity of ST. {ECO:0000250|UniProtKB:P03081}.
CC   -!- MISCELLANEOUS: The strain Dunlop sequence is shown.
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DR   EMBL; V01110; CAA24308.1; -; Genomic_DNA.
DR   EMBL; V01108; CAA24301.1; -; Genomic_DNA.
DR   EMBL; V01109; CAA24303.1; -; Genomic_DNA.
DR   EMBL; M37730; AAA47141.1; -; Genomic_DNA.
DR   EMBL; M37731; AAA47144.1; -; Genomic_DNA.
DR   PIR; D03632; TVVPAB.
DR   RefSeq; YP_717941.1; NC_001538.1. [P03082-1]
DR   AlphaFoldDB; P03082; -.
DR   SMR; P03082; -.
DR   DNASU; 29031012; -.
DR   GeneID; 29031012; -.
DR   KEGG; vg:29031012; -.
DR   OrthoDB; 14669at10239; -.
DR   Proteomes; UP000008475; Segment.
DR   GO; GO:0030430; C:host cell cytoplasm; IEA:UniProtKB-SubCell.
DR   GO; GO:0042025; C:host cell nucleus; ISS:UniProtKB.
DR   GO; GO:0008270; F:zinc ion binding; IEA:UniProtKB-KW.
DR   CDD; cd06257; DnaJ; 1.
DR   FunFam; 1.10.287.110:FF:000161; Small t antigen; 1.
DR   Gene3D; 1.10.287.110; DnaJ domain; 1.
DR   Gene3D; 1.20.120.1860; Small t-antigen, unique domain; 1.
DR   InterPro; IPR001623; DnaJ_domain.
DR   InterPro; IPR036869; J_dom_sf.
DR   InterPro; IPR003354; Papo_T_antigen.
DR   InterPro; IPR036092; Papo_T_antigensf.
DR   Pfam; PF02380; Papo_T_antigen; 1.
DR   SMART; SM00271; DnaJ; 1.
DR   SUPFAM; SSF46565; Chaperone J-domain; 1.
DR   SUPFAM; SSF161240; T-antigen specific domain-like; 1.
DR   PROSITE; PS50076; DNAJ_2; 1.
PE   3: Inferred from homology;
KW   Acetylation; Activator; Alternative splicing; Early protein;
KW   Host cytoplasm; Host nucleus; Host-virus interaction; Metal-binding;
KW   Oncogene; Phosphoprotein; Reference proteome; Transcription;
KW   Transcription regulation; Zinc; Zinc-finger.
FT   CHAIN           1..172
FT                   /note="Small t antigen"
FT                   /id="PRO_0000115053"
FT   DOMAIN          12..75
FT                   /note="J"
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00286"
FT   ZN_FING         101..114
FT                   /note="C4-type; atypical"
FT   ZN_FING         120..141
FT                   /note="H1C3-type; atypical"
FT   MOD_RES         1
FT                   /note="N-acetylmethionine; by host"
FT                   /evidence="ECO:0000250|UniProtKB:P03081"
FT   VARIANT         34
FT                   /note="Missing (in strain: MM)"
FT   VARIANT         100..101
FT                   /note="IC -> MP (in strain: MM)"
FT   VARIANT         102..172
FT                   /note="Missing (in strain: MM)"
SQ   SEQUENCE   172 AA;  20455 MW;  17D55FD9E3EF33DD CRC64;
     MDKVLNREES MELMDLLGLE RAAWGNLPLM RKAYLRKCKE FHPDKGGDED KMKRMNTLYK
     KMEQDVKVAH QPDFGTWSSS EVCADFPLCP DTLYCKEWPI CSKKPSVHCP CMLCQLRLRH
     LNRKFLRKEP LVWIDCYCID CFTQWFGLDL TEETLQWWVQ IIGETPFRDL KL
//