ID   I3_VACCC                Reviewed;         269 AA.
AC   P20499;
DT   01-FEB-1991, integrated into UniProtKB/Swiss-Prot.
DT   01-FEB-1991, sequence version 1.
DT   23-FEB-2022, entry version 68.
DE   RecName: Full=Protein I3;
GN   ORFNames=I3L;
OS   Vaccinia virus (strain Copenhagen) (VACV).
OC   Viruses; Varidnaviria; Bamfordvirae; Nucleocytoviricota; Pokkesviricetes;
OC   Chitovirales; Poxviridae; Chordopoxvirinae; Orthopoxvirus; Vaccinia virus.
OX   NCBI_TaxID=10249;
OH   NCBI_TaxID=9606; Homo sapiens (Human).
RN   [1]
RP   NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
RX   PubMed=2219722; DOI=10.1016/0042-6822(90)90294-2;
RA   Goebel S.J., Johnson G.P., Perkus M.E., Davis S.W., Winslow J.P.,
RA   Paoletti E.;
RT   "The complete DNA sequence of vaccinia virus.";
RL   Virology 179:247-266(1990).
RN   [2]
RP   NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
RA   Goebel S.J., Johnson G.P., Perkus M.E., Davis S.W., Winslow J.P.,
RA   Paoletti E.;
RT   "Appendix to 'The complete DNA sequence of vaccinia virus'.";
RL   Virology 179:517-563(1990).
CC   -!- FUNCTION: Single-stranded DNA (ssDNA)-binding phosphoprotein which
CC       stimulates the enzymatic activity of vaccinia ribonucleotide reductase.
CC       In the absence of magnesium and at low I3 concentration, I3 forms
CC       beaded nucleosome-like structures on ssDNA. In the presence of
CC       magnesium and at high I3 concentration, I3 and DNA aggregate into large
CC       branched filamentous structures. Might be essential for viral parental
CC       DNA replication.
CC   -!- SUBUNIT: Homooctamer (Potential). Homoomultimer (Potential). Interacts
CC       with the small subunit of ribonucleotide reductase; this interaction
CC       stimulates ribonucleotide reductase activity. {ECO:0000305}.
CC   -!- SUBCELLULAR LOCATION: Host cytoplasm {ECO:0000305}. Note=Localizes in
CC       cytoplasmic virus factories, where it is associated with viral DNA.
CC       {ECO:0000305}.
CC   -!- INDUCTION: Expressed in the early phase of the viral replicative cycle.
CC   -!- MISCELLANEOUS: This protein is synthesized in the early as well as at
CC       the intermediate time of infection.
CC   -!- SIMILARITY: Belongs to the chordopoxvirinae I3 family. {ECO:0000305}.
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DR   EMBL; M35027; AAA48058.1; -; Genomic_DNA.
DR   Proteomes; UP000008269; Genome.
DR   GO; GO:0030430; C:host cell cytoplasm; IEA:UniProtKB-SubCell.
DR   GO; GO:0003697; F:single-stranded DNA binding; IEA:InterPro.
DR   GO; GO:0030261; P:chromosome condensation; IEA:UniProtKB-KW.
DR   InterPro; IPR006754; Poxvirus_I3_ssDNA-bd.
DR   Pfam; PF04661; Pox_I3; 1.
DR   PIRSF; PIRSF003767; VAC_I3L; 1.
PE   2: Evidence at transcript level;
KW   DNA condensation; DNA-binding; Early protein; Host cytoplasm;
KW   Reference proteome.
FT   CHAIN           1..269
FT                   /note="Protein I3"
FT                   /id="PRO_0000099571"
SQ   SEQUENCE   269 AA;  29981 MW;  A140A27EFE2B33A2 CRC64;
     MSKVIKKRVE TSPRPTASSD SLQTCAGVIE YAKSISKSNA KCIEYVTLNA SQYANCSSIS
     IKLTDSLSSQ MTSTFIMLEG ETKLYKNKSK QDRSDGYFLK IKVTAASPML YQLLEAVYGN
     IKHKERIPNS LHSLSVETIT EKTFKDESIF INKLNGAMVE YVSAGESSIL RSIEGELESL
     SKRERQLAKA IITPIVFYRS GTETKITFAL KKLIIDREVV ANVIGLSGDS ERVSMTENVE
     EDLARNLGLV DIDDEYDEDS DKEKPIFNV