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Protein

Origin recognition complex subunit 2

Gene

ORC2

Organism
Homo sapiens (Human)
Status
Reviewed-Annotation score: Annotation score: 5 out of 5-Experimental evidence at protein leveli

Functioni

Component of the origin recognition complex (ORC) that binds origins of replication. DNA-binding is ATP-dependent. The specific DNA sequences that define origins of replication have not been identified yet. ORC is required to assemble the pre-replication complex necessary to initiate DNA replication. Binds histone H3 and H4 trimethylation marks H3K9me3, H3K20me3 and H4K27me3. Stabilizes LRWD1, by protecting it from ubiquitin-mediated proteasomal degradation. Also stabilizes ORC3.2 Publications

GO - Molecular functioni

  • DNA replication origin binding Source: ProtInc

GO - Biological processi

  • DNA replication Source: Reactome
  • DNA replication initiation Source: ProtInc
  • G1/S transition of mitotic cell cycle Source: Reactome
  • negative regulation of transcription from RNA polymerase II promoter Source: ProtInc
Complete GO annotation...

Keywords - Biological processi

DNA replication

Enzyme and pathway databases

ReactomeiR-HSA-113507. E2F-enabled inhibition of pre-replication complex formation.
R-HSA-176187. Activation of ATR in response to replication stress.
R-HSA-68616. Assembly of the ORC complex at the origin of replication.
R-HSA-68689. CDC6 association with the ORC:origin complex.
R-HSA-68827. CDT1 association with the CDC6:ORC:origin complex.
R-HSA-68867. Assembly of the pre-replicative complex.
R-HSA-68949. Orc1 removal from chromatin.
R-HSA-68962. Activation of the pre-replicative complex.
R-HSA-69298. Association of licensing factors with the pre-replicative complex.
R-HSA-69300. Removal of licensing factors from origins.
SIGNORiQ13416.

Names & Taxonomyi

Protein namesi
Recommended name:
Origin recognition complex subunit 2
Gene namesi
Name:ORC2
Synonyms:ORC2L
OrganismiHomo sapiens (Human)
Taxonomic identifieri9606 [NCBI]
Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresPrimatesHaplorrhiniCatarrhiniHominidaeHomo
Proteomesi
  • UP000005640 Componenti: Chromosome 2

Organism-specific databases

HGNCiHGNC:8488. ORC2.

Subcellular locationi

GO - Cellular componenti

  • centrosome Source: CACAO
  • condensed chromosome inner kinetochore Source: Ensembl
  • heterochromatin Source: CACAO
  • membrane Source: UniProtKB
  • nuclear chromosome, telomeric region Source: BHF-UCL
  • nuclear origin of replication recognition complex Source: UniProtKB
  • nucleoplasm Source: Reactome
  • nucleus Source: ProtInc
  • origin recognition complex Source: UniProtKB
Complete GO annotation...

Keywords - Cellular componenti

Nucleus

Pathology & Biotechi

Organism-specific databases

PharmGKBiPA32809.

Polymorphism and mutation databases

BioMutaiORC2.
DMDMi8488999.

PTM / Processingi

Molecule processing

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Chaini1 – 577577Origin recognition complex subunit 2PRO_0000127075Add
BLAST

Amino acid modifications

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Modified residuei116 – 1161PhosphothreonineCombined sources
Modified residuei122 – 1221PhosphoserineCombined sources
Modified residuei138 – 1381PhosphoserineCombined sources
Modified residuei226 – 2261PhosphothreonineCombined sources
Modified residuei248 – 2481PhosphoserineCombined sources
Modified residuei280 – 2801PhosphoserineCombined sources

Keywords - PTMi

Phosphoprotein

Proteomic databases

EPDiQ13416.
MaxQBiQ13416.
PaxDbiQ13416.
PeptideAtlasiQ13416.
PRIDEiQ13416.

PTM databases

iPTMnetiQ13416.
PhosphoSiteiQ13416.

Expressioni

Gene expression databases

BgeeiQ13416.
CleanExiHS_ORC2L.
ExpressionAtlasiQ13416. baseline and differential.
GenevisibleiQ13416. HS.

Organism-specific databases

HPAiCAB003693.
HPA034976.

Interactioni

Subunit structurei

Component of ORC, a complex composed of at least 6 subunits: ORC1, ORC2, ORC3, ORC4, ORC5 and ORC6. ORC is regulated in a cell-cycle dependent manner. It is sequentially assembled at the exit from anaphase of mitosis and disassembled as cells enter S phase (PubMed:12909626, PubMed:17716973). Interacts with DBF4 (By similarity). Interacts with MCM10 (PubMed:11095689). Interacts with LRWD1 throughout the cell cycle; this interaction, wich occurs only with non-ubiquitinated form of LRWD1, prevents LRWD1 ubiquitination and hence stabilizes the protein (PubMed:22645314). Interacts with POLQ (PubMed:24989122).By similarity5 Publications

Binary interactionsi

WithEntry#Exp.IntActNotes
CDC5LQ994592EBI-374957,EBI-374880
EBNA1P032116EBI-374957,EBI-996522From a different organism.
FOXM1Q080502EBI-374957,EBI-866480
MCM10Q7L5905EBI-374957,EBI-374912
MCM3P252052EBI-374957,EBI-355153
ORC1Q134158EBI-374957,EBI-374847
ORC4O439296EBI-374957,EBI-374889
ORC5O439138EBI-374957,EBI-374928
TERF2Q155543EBI-374957,EBI-706637

Protein-protein interaction databases

BioGridi111041. 60 interactions.
DIPiDIP-29689N.
IntActiQ13416. 37 interactions.
MINTiMINT-1201828.
STRINGi9606.ENSP00000234296.

Structurei

Secondary structure

1
577
Legend: HelixTurnBeta strand
Show more details
Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Helixi474 – 4818Combined sources
Helixi486 – 50116Combined sources
Turni502 – 5043Combined sources
Helixi513 – 52210Combined sources
Helixi529 – 54113Combined sources
Beta strandi546 – 5494Combined sources
Beta strandi555 – 5584Combined sources
Helixi563 – 57210Combined sources

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
EntryMethodResolution (Å)ChainPositionsPDBsum
5C8HX-ray2.01A458-577[»]
ProteinModelPortaliQ13416.
SMRiQ13416. Positions 292-575.
ModBaseiSearch...
MobiDBiSearch...

Family & Domainsi

Domains and Repeats

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Repeati1 – 100100Involved in LRWD1-bindingAdd
BLAST

Sequence similaritiesi

Belongs to the ORC2 family.Curated

Phylogenomic databases

eggNOGiKOG2928. Eukaryota.
COG5575. LUCA.
GeneTreeiENSGT00390000015228.
HOGENOMiHOG000045588.
HOVERGENiHBG007874.
InParanoidiQ13416.
KOiK02604.
OMAiSAPVCKE.
OrthoDBiEOG7NPFT1.
PhylomeDBiQ13416.
TreeFamiTF101092.

Family and domain databases

InterProiIPR007220. ORC2.
[Graphical view]
PANTHERiPTHR14052. PTHR14052. 1 hit.
PfamiPF04084. ORC2. 1 hit.
[Graphical view]

Sequencei

Sequence statusi: Complete.

Q13416-1 [UniParc]FASTAAdd to basket

« Hide

        10         20         30         40         50
MSKPELKEDK MLEVHFVGDD DVLNHILDRE GGAKLKKERA QLLVNPKKII
60 70 80 90 100
KKPEYDLEED DQEVLKDQNY VEIMGRDVQE SLKNGSATGG GNKVYSFQNR
110 120 130 140 150
KHSEKMAKLA SELAKTPQKS VSFSLKNDPE ITINVPQSSK GHSASDKVQP
160 170 180 190 200
KNNDKSEFLS TAPRSLRKRL IVPRSHSDSE SEYSASNSED DEGVAQEHEE
210 220 230 240 250
DTNAVIFSQK IQAQNRVVSA PVGKETPSKR MKRDKTSDLV EEYFEAHSSS
260 270 280 290 300
KVLTSDRTLQ KLKRAKLDQQ TLRNLLSKVS PSFSAELKQL NQQYEKLFHK
310 320 330 340 350
WMLQLHLGFN IVLYGLGSKR DLLERFRTTM LQDSIHVVIN GFFPGISVKS
360 370 380 390 400
VLNSITEEVL DHMGTFRSIL DQLDWIVNKF KEDSSLELFL LIHNLDSQML
410 420 430 440 450
RGEKSQQIIG QLSSLHNIYL IASIDHLNAP LMWDHAKQSL FNWLWYETTT
460 470 480 490 500
YSPYTEETSY ENSLLVKQSG SLPLSSLTHV LRSLTPNARG IFRLLIKYQL
510 520 530 540 550
DNQDNPSYIG LSFQDFYQQC REAFLVNSDL TLRAQLTEFR DHKLIRTKKG
560 570
TDGVEYLLIP VDNGTLTDFL EKEEEEA
Length:577
Mass (Da):65,972
Last modified:May 30, 2000 - v2
Checksum:iDF3F9C2CF147DA5F
GO

Experimental Info

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Sequence conflicti131 – 1311I → V in AAB33970 (PubMed:8808289).Curated
Sequence conflicti236 – 2361T → L in AAB33970 (PubMed:8808289).Curated
Sequence conflicti392 – 3921I → M in AAB33970 (PubMed:8808289).Curated

Natural variant

Feature keyPosition(s)LengthDescriptionGraphical viewFeature identifierActions
Natural varianti106 – 1061M → K.1 Publication
Corresponds to variant rs2307361 [ dbSNP | Ensembl ].
VAR_014515
Natural varianti521 – 5211R → Q.1 Publication
Corresponds to variant rs16835624 [ dbSNP | Ensembl ].
VAR_021276

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
U40268 mRNA. Translation: AAC50326.2.
U27459 mRNA. Translation: AAB33970.1.
AY652588 Genomic DNA. Translation: AAT46690.1.
AC005037 Genomic DNA. Translation: AAY14725.1.
CH471063 Genomic DNA. Translation: EAW70228.1.
BC014834 mRNA. Translation: AAH14834.1.
CCDSiCCDS2334.1.
RefSeqiNP_006181.1. NM_006190.4.
XP_006712618.1. XM_006712555.2.
UniGeneiHs.444870.

Genome annotation databases

EnsembliENST00000234296; ENSP00000234296; ENSG00000115942.
GeneIDi4999.
KEGGihsa:4999.
UCSCiuc002uwr.4. human.

Keywords - Coding sequence diversityi

Polymorphism

Cross-referencesi

Web resourcesi

NIEHS-SNPs

Sequence databases

Select the link destinations:
EMBLi
GenBanki
DDBJi
Links Updated
U40268 mRNA. Translation: AAC50326.2.
U27459 mRNA. Translation: AAB33970.1.
AY652588 Genomic DNA. Translation: AAT46690.1.
AC005037 Genomic DNA. Translation: AAY14725.1.
CH471063 Genomic DNA. Translation: EAW70228.1.
BC014834 mRNA. Translation: AAH14834.1.
CCDSiCCDS2334.1.
RefSeqiNP_006181.1. NM_006190.4.
XP_006712618.1. XM_006712555.2.
UniGeneiHs.444870.

3D structure databases

Select the link destinations:
PDBei
RCSB PDBi
PDBji
Links Updated
EntryMethodResolution (Å)ChainPositionsPDBsum
5C8HX-ray2.01A458-577[»]
ProteinModelPortaliQ13416.
SMRiQ13416. Positions 292-575.
ModBaseiSearch...
MobiDBiSearch...

Protein-protein interaction databases

BioGridi111041. 60 interactions.
DIPiDIP-29689N.
IntActiQ13416. 37 interactions.
MINTiMINT-1201828.
STRINGi9606.ENSP00000234296.

PTM databases

iPTMnetiQ13416.
PhosphoSiteiQ13416.

Polymorphism and mutation databases

BioMutaiORC2.
DMDMi8488999.

Proteomic databases

EPDiQ13416.
MaxQBiQ13416.
PaxDbiQ13416.
PeptideAtlasiQ13416.
PRIDEiQ13416.

Protocols and materials databases

DNASUi4999.
Structural Biology KnowledgebaseSearch...

Genome annotation databases

EnsembliENST00000234296; ENSP00000234296; ENSG00000115942.
GeneIDi4999.
KEGGihsa:4999.
UCSCiuc002uwr.4. human.

Organism-specific databases

CTDi4999.
GeneCardsiORC2.
HGNCiHGNC:8488. ORC2.
HPAiCAB003693.
HPA034976.
MIMi601182. gene.
neXtProtiNX_Q13416.
PharmGKBiPA32809.
GenAtlasiSearch...

Phylogenomic databases

eggNOGiKOG2928. Eukaryota.
COG5575. LUCA.
GeneTreeiENSGT00390000015228.
HOGENOMiHOG000045588.
HOVERGENiHBG007874.
InParanoidiQ13416.
KOiK02604.
OMAiSAPVCKE.
OrthoDBiEOG7NPFT1.
PhylomeDBiQ13416.
TreeFamiTF101092.

Enzyme and pathway databases

ReactomeiR-HSA-113507. E2F-enabled inhibition of pre-replication complex formation.
R-HSA-176187. Activation of ATR in response to replication stress.
R-HSA-68616. Assembly of the ORC complex at the origin of replication.
R-HSA-68689. CDC6 association with the ORC:origin complex.
R-HSA-68827. CDT1 association with the CDC6:ORC:origin complex.
R-HSA-68867. Assembly of the pre-replicative complex.
R-HSA-68949. Orc1 removal from chromatin.
R-HSA-68962. Activation of the pre-replicative complex.
R-HSA-69298. Association of licensing factors with the pre-replicative complex.
R-HSA-69300. Removal of licensing factors from origins.
SIGNORiQ13416.

Miscellaneous databases

ChiTaRSiORC2. human.
GeneWikiiORC2.
ORC2L.
GenomeRNAii4999.
PROiQ13416.
SOURCEiSearch...

Gene expression databases

BgeeiQ13416.
CleanExiHS_ORC2L.
ExpressionAtlasiQ13416. baseline and differential.
GenevisibleiQ13416. HS.

Family and domain databases

InterProiIPR007220. ORC2.
[Graphical view]
PANTHERiPTHR14052. PTHR14052. 1 hit.
PfamiPF04084. ORC2. 1 hit.
[Graphical view]
ProtoNetiSearch...

Publicationsi

« Hide 'large scale' publications
  1. "Conserved initiator proteins in eukaryotes."
    Gavin K.A., Hidaka M., Stillman B.D.
    Science 270:1667-1671(1995) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA].
  2. Hidaka M., Stillman B.
    Submitted (MAR-1999) to the EMBL/GenBank/DDBJ databases
    Cited for: SEQUENCE REVISION TO 41-42.
  3. "Mouse and human homologues of the yeast origin of replication recognition complex subunit ORC2 and chromosomal localization of the cognate human gene ORC2L."
    Takahara K., Bong M., Brevard R., Eddy R.L., Haley L.L., Sait S.J., Shows T.B., Hoffman G.G., Greenspan D.S.
    Genomics 31:119-122(1996) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [MRNA].
  4. NIEHS SNPs program
    Submitted (JUN-2004) to the EMBL/GenBank/DDBJ databases
    Cited for: NUCLEOTIDE SEQUENCE [GENOMIC DNA], VARIANTS LYS-106 AND GLN-521.
  5. "Generation and annotation of the DNA sequences of human chromosomes 2 and 4."
    Hillier L.W., Graves T.A., Fulton R.S., Fulton L.A., Pepin K.H., Minx P., Wagner-McPherson C., Layman D., Wylie K., Sekhon M., Becker M.C., Fewell G.A., Delehaunty K.D., Miner T.L., Nash W.E., Kremitzki C., Oddy L., Du H.
    , Sun H., Bradshaw-Cordum H., Ali J., Carter J., Cordes M., Harris A., Isak A., van Brunt A., Nguyen C., Du F., Courtney L., Kalicki J., Ozersky P., Abbott S., Armstrong J., Belter E.A., Caruso L., Cedroni M., Cotton M., Davidson T., Desai A., Elliott G., Erb T., Fronick C., Gaige T., Haakenson W., Haglund K., Holmes A., Harkins R., Kim K., Kruchowski S.S., Strong C.M., Grewal N., Goyea E., Hou S., Levy A., Martinka S., Mead K., McLellan M.D., Meyer R., Randall-Maher J., Tomlinson C., Dauphin-Kohlberg S., Kozlowicz-Reilly A., Shah N., Swearengen-Shahid S., Snider J., Strong J.T., Thompson J., Yoakum M., Leonard S., Pearman C., Trani L., Radionenko M., Waligorski J.E., Wang C., Rock S.M., Tin-Wollam A.-M., Maupin R., Latreille P., Wendl M.C., Yang S.-P., Pohl C., Wallis J.W., Spieth J., Bieri T.A., Berkowicz N., Nelson J.O., Osborne J., Ding L., Meyer R., Sabo A., Shotland Y., Sinha P., Wohldmann P.E., Cook L.L., Hickenbotham M.T., Eldred J., Williams D., Jones T.A., She X., Ciccarelli F.D., Izaurralde E., Taylor J., Schmutz J., Myers R.M., Cox D.R., Huang X., McPherson J.D., Mardis E.R., Clifton S.W., Warren W.C., Chinwalla A.T., Eddy S.R., Marra M.A., Ovcharenko I., Furey T.S., Miller W., Eichler E.E., Bork P., Suyama M., Torrents D., Waterston R.H., Wilson R.K.
    Nature 434:724-731(2005) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
  6. Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA].
  7. "The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC)."
    The MGC Project Team
    Genome Res. 14:2121-2127(2004) [PubMed] [Europe PMC] [Abstract]
    Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE MRNA].
    Tissue: Placenta.
  8. "The human homolog of Saccharomyces cerevisiae Mcm10 interacts with replication factors and dissociates from nuclease-resistant nuclear structures in G(2) phase."
    Izumi M., Yanagi K., Mizuno T., Yokoi M., Kawasaki Y., Moon K.Y., Hurwitz J., Yatagai F., Hanaoka F.
    Nucleic Acids Res. 28:4769-4777(2000) [PubMed] [Europe PMC] [Abstract]
    Cited for: INTERACTION WITH MCM10.
  9. "The ORC1 cycle in human cells: II. Dynamic changes in the human ORC complex during the cell cycle."
    Ohta S., Tatsumi Y., Fujita M., Tsurimoto T., Obuse C.
    J. Biol. Chem. 278:41535-41540(2003) [PubMed] [Europe PMC] [Abstract]
    Cited for: IDENTIFICATION IN THE ORC COMPLEX, IDENTIFICATION BY MASS SPECTROMETRY, ASSEMBLY OF THE ORC COMPLEX.
  10. "ATP-dependent assembly of the human origin recognition complex."
    Siddiqui K., Stillman B.
    J. Biol. Chem. 282:32370-32383(2007) [PubMed] [Europe PMC] [Abstract]
    Cited for: RECONSTITUTION OF THE ORC COMPLEX, DISASSEMBLY OF THE ORC COMPLEX.
  11. Cited for: PHOSPHORYLATION [LARGE SCALE ANALYSIS] AT THR-116 AND SER-280, IDENTIFICATION BY MASS SPECTROMETRY [LARGE SCALE ANALYSIS].
    Tissue: Cervix carcinoma.
  12. "Quantitative phosphoproteomics reveals widespread full phosphorylation site occupancy during mitosis."
    Olsen J.V., Vermeulen M., Santamaria A., Kumar C., Miller M.L., Jensen L.J., Gnad F., Cox J., Jensen T.S., Nigg E.A., Brunak S., Mann M.
    Sci. Signal. 3:RA3-RA3(2010) [PubMed] [Europe PMC] [Abstract]
    Cited for: PHOSPHORYLATION [LARGE SCALE ANALYSIS] AT THR-116; SER-122; SER-138 AND THR-226, IDENTIFICATION BY MASS SPECTROMETRY [LARGE SCALE ANALYSIS].
    Tissue: Cervix carcinoma.
  13. Cited for: IDENTIFICATION BY MASS SPECTROMETRY [LARGE SCALE ANALYSIS].
  14. "Orc2 protects ORCA from ubiquitin-mediated degradation."
    Shen Z., Prasanth S.G.
    Cell Cycle 11:3578-3589(2012) [PubMed] [Europe PMC] [Abstract]
    Cited for: FUNCTION, INTERACTION WITH LRWD1.
  15. "Leucine-rich repeat and WD repeat-containing protein 1 is recruited to pericentric heterochromatin by trimethylated lysine 9 of histone H3 and maintains heterochromatin silencing."
    Chan K.M., Zhang Z.
    J. Biol. Chem. 287:15024-15033(2012) [PubMed] [Europe PMC] [Abstract]
    Cited for: FUNCTION, BINDING TO HISTONE H3 AND H4 TRIMETHYLATION MARKS.
  16. "Dynamic association of ORCA with prereplicative complex components regulates DNA replication initiation."
    Shen Z., Chakraborty A., Jain A., Giri S., Ha T., Prasanth K.V., Prasanth S.G.
    Mol. Cell. Biol. 32:3107-3120(2012) [PubMed] [Europe PMC] [Abstract]
    Cited for: INTERACTION WITH LRWD1.
  17. "Toward a comprehensive characterization of a human cancer cell phosphoproteome."
    Zhou H., Di Palma S., Preisinger C., Peng M., Polat A.N., Heck A.J., Mohammed S.
    J. Proteome Res. 12:260-271(2013) [PubMed] [Europe PMC] [Abstract]
    Cited for: PHOSPHORYLATION [LARGE SCALE ANALYSIS] AT THR-116; THR-226; SER-248 AND SER-280, IDENTIFICATION BY MASS SPECTROMETRY [LARGE SCALE ANALYSIS].
    Tissue: Cervix carcinoma and Erythroleukemia.
  18. Cited for: INTERACTION WITH POLQ.

Entry informationi

Entry nameiORC2_HUMAN
AccessioniPrimary (citable) accession number: Q13416
Secondary accession number(s): Q13204, Q53TX5
Entry historyi
Integrated into UniProtKB/Swiss-Prot: November 1, 1997
Last sequence update: May 30, 2000
Last modified: July 6, 2016
This is version 136 of the entry and version 2 of the sequence. [Complete history]
Entry statusiReviewed (UniProtKB/Swiss-Prot)
Annotation programChordata Protein Annotation Program
DisclaimerAny medical or genetic information present in this entry is provided for research, educational and informational purposes only. It is not in any way intended to be used as a substitute for professional medical advice, diagnosis, treatment or care.

Miscellaneousi

Keywords - Technical termi

3D-structure, Complete proteome, Reference proteome

Documents

  1. Human chromosome 2
    Human chromosome 2: entries, gene names and cross-references to MIM
  2. Human entries with polymorphisms or disease mutations
    List of human entries with polymorphisms or disease mutations
  3. Human polymorphisms and disease mutations
    Index of human polymorphisms and disease mutations
  4. MIM cross-references
    Online Mendelian Inheritance in Man (MIM) cross-references in UniProtKB/Swiss-Prot
  5. PDB cross-references
    Index of Protein Data Bank (PDB) cross-references
  6. SIMILARITY comments
    Index of protein domains and families

Similar proteinsi

Links to similar proteins from the UniProt Reference Clusters (UniRef) at 100%, 90% and 50% sequence identity:
100%UniRef100 combines identical sequences and sub-fragments with 11 or more residues from any organism into one UniRef entry.
90%UniRef90 is built by clustering UniRef100 sequences that have at least 90% sequence identity to, and 80% overlap with, the longest sequence (a.k.a seed sequence).
50%UniRef50 is built by clustering UniRef90 seed sequences that have at least 50% sequence identity to, and 80% overlap with, the longest sequence in the cluster.