SBH1/YER087C-B Summary Help

Standard Name SBH1 1
Systematic Name YER087C-B
Alias SEB1 , YER087C-A
Feature Type ORF, Verified
Description Beta subunit of Sec61p ER translocation complex (Sec61p-Sss1p-Sbh1p); involved in protein translocation into the endoplasmic reticulum; interacts with the exocyst complex and also with Rtn1p; cotranslationally N-acetylated by NatA; SBH1 has a paralog, SBH2, that arose from the whole genome duplication (2, 3, 4, 5, 6 and see Summary Paragraph)
Name Description Sec61 beta homolog 1 1
Chromosomal Location
ChrV:332830 to 332582 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Gene Ontology Annotations All SBH1 GO evidence and references
  View Computational GO annotations for SBH1
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 117 genes
Classical genetics
Large-scale survey
141 total interaction(s) for 88 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 5
  • Affinity Capture-RNA: 2
  • Affinity Capture-Western: 21
  • Co-purification: 2
  • PCA: 18
  • Reconstituted Complex: 1
  • Two-hybrid: 5

Genetic Interactions
  • Dosage Rescue: 8
  • Negative Genetic: 68
  • Phenotypic Enhancement: 3
  • Positive Genetic: 1
  • Synthetic Growth Defect: 4
  • Synthetic Lethality: 3

Expression Summary
Length (a.a.) 82
Molecular Weight (Da) 8,711
Isoelectric Point (pI) 11.31
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrV:332830 to 332582 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..249 332830..332582 2011-02-03 1996-07-31
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000002128

SBH1 encodes the beta subunit of the heterotrimeric Sec61 complex, also referred to as the translocon (1, reviewed in 7). The Sec61 complex forms a channel in the endoplasmic reticulum (ER) membrane and mediates translocation of secretory and membrane proteins into the ER and also retrograde transport of misfolded proteins to the cytoplasm for degradation (reviewed in 8 and 7). The other subunits of the Sec61 complex are Sec61p, a 10-transmembrane domain protein that is the major translocon subunit, and Sss1p, a small essential protein thought to stabilize the complex (9, 10, 11).

Proteins that are transported into or across the ER membrane are directed there by signal sequences or by transmembrane segments that interact with the translocation apparatus. In S. cerevisiae the Sec61 complex mediates both co- and posttranslational translocation (while the mammalian Sec61 complex functions primarily with the cotranslational pathway; 12). During cotranslational translocation, ribosomes synthesizing signal sequence-containing proteins are targeted to the translocon via the signal recognition particle (SRP), and the ribosomes bind directly to Sec61p such that protein biosynthesis and translocation are synchronous (13). Posttranslational translocation requires Sec62p, Sec63p, Sec66p, and Sec72p (comprising the Sec63 complex), as well as Kar2p, in place of SRP to facilitate interaction of the full-length polypeptide with the translocon via the signal sequence (14, 1).

Retrograde transport of misfolded proteins into the cytoplasm (also called dislocation) employs the Sec61 channel via interaction with the 19S proteasome regulatory particle (15). This interaction, which competes with the ribosome-Sec61p interaction, defines the Sec61 complex as the principal proteasome receptor in the ER membrane (15).

Sbh1p is a small protein with a single C-terminal transmembrane domain, and an N-terminal cytosolic region that has guanine nucleotide exchange factor (GEF) activity (2, 16). In contrast to the inviability conferred by null mutations in either SEC61 or SSS1, sbh1 null mutations do not cause a growth defect (17, 18, 19), and an sbh1 sbh2 double null mutant exhibits temperature (heat)-sensitive growth (19). Expression of the 25-amino acid transmembrane domain alone rescues the ts growth defect of the double null mutant, and this domain is sufficient for interaction with Sec61p and Sss1p to form the Sec61 complex (5).

Physical interactions between Sbh1p and components of the exocyst complex, the oligosaccharyltransferase complex, and the signal peptidase complex have been reported (20, 21, 3, 5). Sbh1p is conserved among organisms; it is termed Sec61 beta in mammals, SecG in eubacteria, and Secbeta in archaea (reviewed in 22).

Last updated: 2007-11-09 Contact SGD

References cited on this page View Complete Literature Guide for SBH1
1) Panzner S, et al.  (1995) Posttranslational protein transport in yeast reconstituted with a purified complex of Sec proteins and Kar2p. Cell 81(4):561-70
2) Toikkanen J, et al.  (1996) Yeast protein translocation complex: isolation of two genes SEB1 and SEB2 encoding proteins homologous to the Sec61 beta subunit. Yeast 12(5):425-38
3) Toikkanen JH, et al.  (2003) The beta subunit of the Sec61p endoplasmic reticulum translocon interacts with the exocyst complex in Saccharomyces cerevisiae. J Biol Chem 278(23):20946-53
4) Byrne KP and Wolfe KH  (2005) The Yeast Gene Order Browser: combining curated homology and syntenic context reveals gene fate in polyploid species. Genome Res 15(10):1456-61
5) Feng D, et al.  (2007) The transmembrane domain is sufficient for Sbh1p function, its association with the Sec61 complex, and interaction with Rtn1p. J Biol Chem 282(42):30618-28
6) Soromani C, et al.  (2012) N-acetylation and phosphorylation of Sec complex subunits in the ER membrane. BMC Cell Biol 13(1):34
7) Romisch K  (1999) Surfing the Sec61 channel: bidirectional protein translocation across the ER membrane. J Cell Sci 112 ( Pt 23)():4185-91
8) Sommer T and Wolf DH  (1997) Endoplasmic reticulum degradation: reverse protein flow of no return. FASEB J 11(14):1227-33
9) Esnault Y, et al.  (1994) SSS1 encodes a stabilizing component of the Sec61 subcomplex of the yeast protein translocation apparatus. J Biol Chem 269(44):27478-85
10) Wilkinson BM, et al.  (1997) Molecular architecture of the ER translocase probed by chemical crosslinking of Sss1p to complementary fragments of Sec61p. EMBO J 16(15):4549-59
11) Wilkinson BM, et al.  (1996) Determination of the transmembrane topology of yeast Sec61p, an essential component of the endoplasmic reticulum translocation complex. J Biol Chem 271(41):25590-7
12) Ng DT, et al.  (1996) Signal sequences specify the targeting route to the endoplasmic reticulum membrane. J Cell Biol 134(2):269-78
13) Prinz A, et al.  (2000) Sec61p is the main ribosome receptor in the endoplasmic reticulum of Saccharomyces cerevisiae. Biol Chem 381(9-10):1025-9
14) Plath K, et al.  (1998) Signal sequence recognition in posttranslational protein transport across the yeast ER membrane. Cell 94(6):795-807
15) Kalies KU, et al.  (2005) The protein translocation channel binds proteasomes to the endoplasmic reticulum membrane. EMBO J 24(13):2284-93
16) Helmers J, et al.  (2003) The beta-subunit of the protein-conducting channel of the endoplasmic reticulum functions as the guanine nucleotide exchange factor for the beta-subunit of the signal recognition particle receptor. J Biol Chem 278(26):23686-90
17) Deshaies RJ and Schekman R  (1987) A yeast mutant defective at an early stage in import of secretory protein precursors into the endoplasmic reticulum. J Cell Biol 105(2):633-45
18) Esnault Y, et al.  (1993) The yeast SSS1 gene is essential for secretory protein translocation and encodes a conserved protein of the endoplasmic reticulum. EMBO J 12(11):4083-93
19) Finke K, et al.  (1996) A second trimeric complex containing homologs of the Sec61p complex functions in protein transport across the ER membrane of S. cerevisiae. EMBO J 15(7):1482-94
20) Antonin W, et al.  (2000) Interactions between Spc2p and other components of the endoplasmic reticulum translocation sites of the yeast Saccharomyces cerevisiae. J Biol Chem 275(44):34068-72
21) Chavan M, et al.  (2005) Subunits of the translocon interact with components of the oligosaccharyl transferase complex. J Biol Chem 280(24):22917-24
22) Osborne AR, et al.  (2005) Protein translocation by the Sec61/SecY channel. Annu Rev Cell Dev Biol 21():529-50