ID   TERS_BPP21              Reviewed;         182 AA.
AC   P68654; P36694;
DT   07-DEC-2004, integrated into UniProtKB/Swiss-Prot.
DT   07-DEC-2004, sequence version 1.
DT   03-AUG-2022, entry version 51.
DE   RecName: Full=Terminase, small subunit;
DE   AltName: Full=Gp1;
GN   Name=1; Synonyms=nohA;
OS   Enterobacteria phage P21 (Bacteriophage 21) (Bacteriophage P21).
OC   Viruses; Duplodnaviria; Heunggongvirae; Uroviricota; Caudoviricetes;
OC   Caudovirales; Siphoviridae; Lambdavirus.
OX   NCBI_TaxID=10711;
OH   NCBI_TaxID=562; Escherichia coli.
RN   [1]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RX   PubMed=3159906; DOI=10.1016/0022-2836(85)90217-7;
RA   Miller G., Feiss M.;
RT   "Sequence of the left end of phage 21 DNA.";
RL   J. Mol. Biol. 183:246-249(1985).
RN   [2]
RP   NUCLEOTIDE SEQUENCE [GENOMIC DNA].
RX   PubMed=8468297; DOI=10.1128/jb.175.8.2393-2399.1993;
RA   Smith M.P., Feiss M.;
RT   "Sites and gene products involved in lambdoid phage DNA packaging.";
RL   J. Bacteriol. 175:2393-2399(1993).
CC   -!- FUNCTION: Component of the terminase that processes and encapsidates
CC       viral genomes during virion assembly. The terminase is composed of two
CC       small and one large subunits. To initiate packaging, it binds a
CC       specific sequence, at the junction of adjacent viral genomes in the
CC       concatemeric DNA substrate. Next, in a reaction stimulated by the
CC       presence of proheads and ATP but not requiring ATP hydrolysis, the
CC       terminase creates two nicks at a specific site, one on each stand.
CC       Terminase then separates the cohesive ends in a reaction requiring ATP
CC       hydrolysis. The heterotrimer remains bound to the left end of the
CC       genome to be packaged, forming a stable DNA-protein complex known as
CC       complex I. In a reaction facilitated by a viral assembly catalyst,
CC       gpFI, complex I binds a prohead, a preformed head shell precursor, to
CC       form complex II. In another packaging reaction requiring ATP
CC       hydrolysis, the DNA is translocated into the prohead until the next
CC       specific site on the concatemer reaches the packaging complex. At this
CC       time the downstream specific site is cut and the heterotrimer undocks
CC       from the DNA-filled head to remain bound to the left end of
CC       concatemer's next genome. The new heterotrimer-DNA complex I binds
CC       another prohead to continue the processive, polarized packaging of
CC       viral genomes. The terminase is dependent upon host integration host
CC       factor (ihfA/ihfB) for these activities.
CC       {ECO:0000250|UniProtKB:P03707}.
CC   -!- SUBUNIT: Heterotrimer of two small and one large terminase subunits.
CC       The active complex may be composed of five heterotrimers.
CC       {ECO:0000250|UniProtKB:P03707}.
CC   -!- SUBCELLULAR LOCATION: Host cytoplasm {ECO:0000250|UniProtKB:P03707}.
CC   -!- SIMILARITY: Belongs to the terminase small subunit family.
CC       {ECO:0000305}.
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DR   EMBL; M23775; AAA32337.1; -; Genomic_DNA.
DR   EMBL; M81255; AAA32339.1; -; Genomic_DNA.
DR   EMBL; X02501; CAA26342.1; -; Genomic_DNA.
DR   PDB; 7LWR; X-ray; 2.35 A; A/B/C/D/E/F/G/H=1-54.
DR   PDBsum; 7LWR; -.
DR   SMR; P68654; -.
DR   GO; GO:0030430; C:host cell cytoplasm; IEA:UniProtKB-SubCell.
DR   GO; GO:0005524; F:ATP binding; IEA:UniProtKB-KW.
DR   GO; GO:0003677; F:DNA binding; IEA:UniProtKB-KW.
DR   Gene3D; 1.10.10.10; -; 1.
DR   InterPro; IPR009061; DNA-bd_dom_put_sf.
DR   InterPro; IPR010906; Phage_lambda_Nu1_terminase-ssu.
DR   InterPro; IPR036388; WH-like_DNA-bd_sf.
DR   Pfam; PF07471; Phage_Nu1; 1.
DR   SUPFAM; SSF46955; SSF46955; 1.
PE   1: Evidence at protein level;
KW   3D-structure; ATP-binding; Coiled coil; DNA-binding; Host cytoplasm;
KW   Nucleotide-binding; Viral genome packaging; Viral release from host cell.
FT   CHAIN           1..182
FT                   /note="Terminase, small subunit"
FT                   /id="PRO_0000077676"
FT   COILED          51..105
FT                   /evidence="ECO:0000255"
FT   BINDING         31..36
FT                   /ligand="ATP"
FT                   /ligand_id="ChEBI:CHEBI:30616"
FT                   /evidence="ECO:0000250"
SQ   SEQUENCE   182 AA;  20507 MW;  E3EBD9DCA6820284 CRC64;
     MKVNKKRLAE IFNVDPRTIE RWQSQGLPCA SKGSKGIESV FDTAMAIQWY AQRETDIENE
     KLRKELDDLR AAAESDLQPG TIDYERYRLT KAQADAQELK NAREDGVVLE TELFTFILQR
     VAQEISGILV RVPLTLQRKY PDISPSHLDV VKTEIAKASN VAAKAGENVG GWIDDFRRAE
     GS