Pathway Human Homo sapiens

Complex III assembly

R-HSA-9865881 in Reactome release 97: under Respiratory electron transport, with 26 genes placed in it by the mapping files and 0 child pathways in the hierarchy.

The same number in the other species

Reactome writes the mouse and rat events it infers from a human pathway under the human number with the species token. A door opens only where that species' own list in this release holds the id: R-MMU-9865881 (mouse), R-RNO-9865881 (rat). Whether the event was inferred from this one is what the record says.

The record
The genes
Parents and children

Scripts are off

This page reads the pathway's record from its source while you read the rest; with scripts off the card stays at its loading line. Reload with scripts on to see it, or open the source's own page from the link in the card.

01The record

Reactome's own record of this pathway

What this tells you

The pathway list, the hierarchy and the genes on this page are read from the files Reactome publishes for Reactome release 97, built into this site on 2026-09-09: the pathway list, the hierarchy relationship file and the two gene mapping files. The record card is the one live read, Reactome's own record of this pathway.

Reactome's download page describes the mapping files: Mapping files link the source database identifier to the lowest level pathway diagram or subset of the pathway, all levels of the pathway hierarchy or database identifier to all reactions. [R13] The gene list here is the all-levels mapping of NCBI Gene ids, filled from the all-levels mapping of Ensembl ids where the NCBI file has no row for a gene; each row names which file it came from by the shape of its source id. Each row carries the evidence codes the file writes for it, as written and unranked, and both where the file writes both; no page of Reactome's documentation the survey read defines the codes, so this page does not expand them. A gene id the identity files do not name is kept as the source's own id with no door rather than turned into a symbol.

On citing what a search finds, Reactome says: It should be remembered that while we strive to contain the most current and accurate data, Reactome should not be used in citations where other primary sources of information are available. [R12] The record card prints the literature Reactome attaches to a curated pathway for that reason. The data are public domain: All data in the Reactome database and files derived from that data are licensed under the Creative Commons Public Domain Dedication (CC0). User may copy, modify, and distribute these data, even for commercial purposes, without asking for permission. Attribution is encouraged but not required. [R10] The pathway illustrations are licensed apart, under CC BY 4.0, and none is shown here.

A gene on this list is one Reactome places in this pathway in this release, and that is all the row says: it does not say the gene is expressed in a tissue or associated with a disease, which are the other two explorers' questions, read from other sources. Reactome's papers of record are [R01] [R02].

[R01] Ragueneau E, Gong C, Sinquin P, Sevilla C, Beavers D, Grentner A, et al. (2026). The Reactome Knowledgebase 2026. Nucleic Acids Research 54:D673-D681. PMID 41251150, doi 10.1093/nar/gkaf1223.
[R02] Milacic M, Beavers D, Conley P, Gong C, Gillespie M, Griss J, et al. (2024). The Reactome Pathway Knowledgebase 2024. Nucleic Acids Research 52:D672-D678. PMID 37941124, doi 10.1093/nar/gkad1025.
[R10] Reactome, reactome.org. License Agreement. https://reactome.org/license, read 2026-09-09.
[R12] Reactome, reactome.org. Citing us. https://reactome.org/cite, read 2026-09-09.
[R13] Reactome, reactome.org. Download. https://reactome.org/download-data, read 2026-09-09.

Stable id: R-HSA-9865881.2
Class: Pathway
Species: Homo sapiens (human)
Inferred: yes
Disease pathway: no
Released: 2024-06-15
Events inside: 10, counted from the record

Reactome's caveat

The electronically inferred reactions presented in Reactome are thus not data, but hypotheses useful to direct the design of confirmatory experiments.
Reactome, on its computationally inferred events.

Assembly of the cytochrome c (cytochrome bc1) reductase (Complex III) was mainly investigated in yeast. The process in humans is considered to recapitulate the process in the yeast system based on the high similarity in structure and composition of the yeast and human complexes. Human Complex III probably consists of two identical sub-complexes, each containing at least 11 subunits: the catalytic core containing cytochrome b (MT-CYTB), cytochrome c1 (CYC1), and the Rieske protein (UQCRFS1), as well as the additional subunits UQCRC1, UQCRC2, UQCRC10, UQCRC11, UQCRCB, UQCRCH, UQCRCQ (Guo et al., 2017; Dennerlein et al., 2021; reviewed in Ndi et al., 2018; Signes & Fernandez-Vizarra, 2018). While complex I, III, and IV form a supercomplex, there is no evidence of any physiological advantage of this configuration (reviewed in Kohler et al., 2023; Brischigliaro et al., 2023). Mutations in nuclear genes coding for subunits of Complex III, as well as assembly factors, can cause complex III deficiency (MC3D; reviewed in Fernández-Vizarra & Zeviani, 2015).

Literature Reactome attaches

Assembly of mammalian oxidative phosphorylation complexes I-V and supercomplexesEssays Biochem, 2018, vol. 62, p. 255-270PubMed 30030361
Defining the interactome of the human mitochondrial ribosome identifies SMIM4 and TMEM223 as respiratory chain assembly factors

Reading this pathway's record from Reactome (the pathway record).Still reading. A first read of a pathway can take a while; this page waits up to 35 seconds for it, and its scripts then bring in the panel, or a line saying what did not arrive.

02The genes

Genes Reactome places in this human pathway

The mapping files place 26 genes in this human pathway; showing 1 to 26, in pages of 100, sorted by symbol for reading. The order carries no ranking.

Genes Reactome places in this human pathway, page 1 of 1
Gene	Authority id	Mapping file id	Evidence codes
GeneBCS1L	AuthorityHGNC:1020	Mapping file id617 NCBI file	EvidenceIEA
GeneCYC1	AuthorityHGNC:2579	Mapping file id1537 NCBI file	EvidenceIEA, TAS
GeneFXN	AuthorityHGNC:3951	Mapping file id2395 NCBI file	EvidenceTAS
GeneHSCB	AuthorityHGNC:28913	Mapping file id150274 NCBI file	EvidenceTAS
GeneHSPA9	AuthorityHGNC:5244	Mapping file id3313 NCBI file	EvidenceTAS
GeneISCU	AuthorityHGNC:29882	Mapping file id23479 NCBI file	EvidenceTAS
GeneLETM1	AuthorityHGNC:6556	Mapping file id3954 NCBI file	EvidenceIEA
GeneLYRM4	AuthorityHGNC:21365	Mapping file id57128 NCBI file	EvidenceTAS
GeneLYRM7	AuthorityHGNC:28072	Mapping file id90624 NCBI file	EvidenceTAS
GeneMT-CYB	AuthorityHGNC:7427	Mapping file id4519 NCBI file	EvidenceIEA, TAS
GeneNFS1	AuthorityHGNC:15910	Mapping file id9054 NCBI file	EvidenceTAS
GeneTTC19	AuthorityHGNC:26006	Mapping file id54902 NCBI file	EvidenceTAS
GeneUQCC1	AuthorityHGNC:15891	Mapping file id55245 NCBI file	EvidenceIEA
GeneUQCC2	AuthorityHGNC:21237	Mapping file id84300 NCBI file	EvidenceIEA
GeneUQCC3	AuthorityHGNC:34399	Mapping file id790955 NCBI file	EvidenceIEA
GeneUQCC5	AuthorityHGNC:37257	Mapping file id440957 NCBI file	EvidenceIEA
GeneUQCC6	AuthorityHGNC:34450	Mapping file id728568 NCBI file	EvidenceIEA
GeneUQCR10	AuthorityHGNC:30863	Mapping file id29796 NCBI file	EvidenceIEA, TAS
GeneUQCR11	AuthorityHGNC:30862	Mapping file id10975 NCBI file	EvidenceIEA, TAS
GeneUQCRB	AuthorityHGNC:12582	Mapping file id7381 NCBI file	EvidenceIEA, TAS
GeneUQCRC1	AuthorityHGNC:12585	Mapping file id7384 NCBI file	EvidenceIEA, TAS
GeneUQCRC2	AuthorityHGNC:12586	Mapping file id7385 NCBI file	EvidenceIEA, TAS
GeneUQCRFS1	AuthorityHGNC:12587	Mapping file id7386 NCBI file	EvidenceIEA, TAS
GeneUQCRH	AuthorityHGNC:12590	Mapping file id7388 NCBI file	EvidenceIEA, TAS
GeneUQCRHL	AuthorityHGNC:51714	Mapping file id440567 NCBI file	EvidenceIEA, TAS
GeneUQCRQ	AuthorityHGNC:29594	Mapping file id27089 NCBI file	EvidenceIEA, TAS

Evidence codes on this page: IEA, TAS, as the mapping file writes them; a row carrying two was written twice by the file, once under each. The mapping file id says which file placed the gene: an NCBI Gene id from NCBI2Reactome_All_Levels.txt, an Ensembl gene id from Ensembl2Reactome_All_Levels.txt. The two files can disagree about a code, so a row's codes are the one file's view. Measured by this site's build over this release on 2026-09-09: of the 138,908 human pathway-gene pairs both files place, 207 (0.149 per cent, over 47 genes) carry TAS in the Ensembl file where the NCBI rows carry IEA alone.

Reactome mapping files, the human rows for this pathway · Reactome release 97 · read 2026-09-09 · Reactome downloads"NCBI2Reactome_All_Levels.txt" and "Ensembl2Reactome_All_Levels.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.

03The hierarchy

Parents and children in this release's hierarchy

Parents

Respiratory electron transportR-HSA-611105159 genes

Children

None: no pathway of this release's list names this one as a parent.

Reactome's hierarchy is a graph rather than a tree: a pathway can sit under more than one parent, and the gene counts are each pathway's own placements at every level under it, so a parent's count is not the sum of its children's.

Reactome, the human pathway list and hierarchy relationship file · Reactome release 97 · read 2026-09-09 · Reactome downloads"ReactomePathways.txt" and "ReactomePathwaysRelation.txt", Reactome, release 97, https://reactome.org/download-data/ (date of access 2026-09-09). Data CC0; attribution encouraged.