SAM35/YHR083W Summary Help

Standard Name SAM35 1
Systematic Name YHR083W
Alias FMP20 , TOB38 2 , TOM38 3
Feature Type ORF, Verified
Description Component of the sorting and assembly machinery (SAM) complex; the SAM (or TOB) complex is located in the mitochondrial outer membrane; the complex binds precursors of beta-barrel proteins and facilitates their insertion into the outer membrane (1, 2, 3, 4 and see Summary Paragraph)
Name Description Sorting and Assembly Machinery 1
Chromosomal Location
ChrVIII:272627 to 273616 | ORF Map | GBrowse
Gene Ontology Annotations All SAM35 GO evidence and references
  View Computational GO annotations for SAM35
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 12 genes
Classical genetics
Large-scale survey
reduction of function
74 total interaction(s) for 45 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 1
  • Affinity Capture-RNA: 4
  • Affinity Capture-Western: 34
  • Co-fractionation: 1
  • Co-purification: 1
  • PCA: 3
  • Reconstituted Complex: 1
  • Two-hybrid: 2

Genetic Interactions
  • Dosage Rescue: 2
  • Negative Genetic: 23
  • Positive Genetic: 2

Expression Summary
Length (a.a.) 329
Molecular Weight (Da) 37,404
Isoelectric Point (pI) 7.13
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrVIII:272627 to 273616 | ORF Map | GBrowse
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..990 272627..273616 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 SGDIDS000001125

About mitochondrial import

While the mitochondrial genome encodes a handful of proteins, most of the hundreds of proteins that reside in the mitochondrion are encoded by nuclear genes, translated in the cytoplasm, and imported into mitochondria via a series of complex molecular machines (see 5, 6 for review). Many of the proteins imported into mitochondria are involved in respiration, which is not an essential process: S. cerevisiae is able to carry out either fermentative growth on carbon sources such as glucose, or respiratory growth on nonfermentable carbon sources such as glycerol and ethanol. However, since maintenance of the mitochondrial compartment is essential to life, mutations that completely disrupt mitochondrial import are lethal.

about the SAM complex

The sorting and assembly machinery (SAM) complex, also known as the translocase of outer membrane beta-barrel proteins (TOB), is required for the correct insertion of beta-barrel proteins into the mitochondrial outer membrane (7). The core of this complex, which is located in the outer membrane, is composed of Sam50p/Tob55p, itself a beta-barrel protein; Sam37p/Mas37p; and Sam35p/Tob38p (8, 9, 1, 2, 3). Mdm10p, a protein first discovered for its role in mitochondrial morphology, also associates with the SAM complex (10).

Beta-barrel proteins are first translocated across the outer membrane by the translocase of the outer mitochondrial membrane (TOM) complex. After transit through the TOM complex into the intermembrane space, both of the complexes of small TIM proteins that reside there (Tim8p-Tim13p complex and Tim9p-Tim10p) are involved in delivery of the beta-barrel proteins to the SAM complex (11). The SAM complex then mediates insertion of the proteins into the mitochondrial outer membrane (12). The final steps of the process require Mdm10p as well as two other proteins implicated in maintenance of mitochondrial morphology, Mdm12p and Mmm1p, which themselves form a complex with Mdm10p (10). In addition to Sam50p/Tob55p, the beta-barrel proteins imported by this route include porin (Por1p or VDAC), the most abundant outer membrane protein; Mdm10p; and Tom40p, which comprises the pore of the TOM complex. All of these substrate proteins have a SAM complex recognition motif termed the beta-signal (12). The SAM complex is also required for correct insertion of some other subunits of the TOM complex, which do not have a beta-barrel structure, into the outer membrane: the entire complex is required for assembly of Tom22p into the TOM complex, while Sam37p only is required for assembly of Tom5p, Tom6p, and Tom7p (13).

about SAM35

Sam35p is an essential constituent of the SAM complex, but is not strongly conserved beyond the fungi although it has weak similarity to the mammalian mitochondrial protein metaxin (2, 1, 3). Its submitochondrial location is disputed: several initial studies identified it as a peripheral protein on the cytosolic face of the outer membrane (2, 1, 3) but a later study suggests that it is embedded in the outer membrane via protein-protein interactions with Sam50p and may extend into the intermembrane space (12). Sam35p has been shown to have a role in the recognition of beta-barrel precursor proteins. Temperature-sensitive sam35 mutants display decreased binding of precursor proteins to the SAM complex (14), and Sam35p binds directly to precursor proteins (2, 12). Both of these observations lend support to the idea that at least part of Sam35p is in the same environment as beta-barrel precursors (14, 12).

Last updated: 2009-03-17 Contact SGD

References cited on this page View Complete Literature Guide for SAM35
1) Milenkovic D, et al.  (2004) Sam35 of the mitochondrial protein sorting and assembly machinery is a peripheral outer membrane protein essential for cell viability. J Biol Chem 279(21):22781-5
2) Waizenegger T, et al.  (2004) Tob38, a novel essential component in the biogenesis of beta-barrel proteins of mitochondria. EMBO Rep 5(7):704-9
3) Ishikawa D, et al.  (2004) Two novel proteins in the mitochondrial outer membrane mediate beta-barrel protein assembly. J Cell Biol 166(5):621-7
4) Habib SJ, et al.  (2005) Assembly of the TOB complex of mitochondria. J Biol Chem 280(8):6434-40
5) Neupert W and Herrmann JM  (2007) Translocation of proteins into mitochondria. Annu Rev Biochem 76:723-49
6) Mokranjac D and Neupert W  (2009) Thirty years of protein translocation into mitochondria: unexpectedly complex and still puzzling. Biochim Biophys Acta 1793(1):33-41
7) Paschen SA, et al.  (2005) Biogenesis of beta-barrel membrane proteins of mitochondria. Trends Biochem Sci 30(10):575-82
8) Kozjak V, et al.  (2003) An essential role of Sam50 in the protein sorting and assembly machinery of the mitochondrial outer membrane. J Biol Chem 278(49):48520-3
9) Wiedemann N, et al.  (2003) Machinery for protein sorting and assembly in the mitochondrial outer membrane. Nature 424(6948):565-71
10) Meisinger C, et al.  (2007) The morphology proteins Mdm12/Mmm1 function in the major beta-barrel assembly pathway of mitochondria. EMBO J 26(9):2229-39
11) Wiedemann N, et al.  (2004) Biogenesis of the protein import channel Tom40 of the mitochondrial outer membrane: intermembrane space components are involved in an early stage of the assembly pathway. J Biol Chem 279(18):18188-94
12) Kutik S, et al.  (2008) Dissecting membrane insertion of mitochondrial beta-barrel proteins. Cell 132(6):1011-24
13) Stojanovski D, et al.  (2007) Alternative function for the mitochondrial SAM complex in biogenesis of alpha-helical TOM proteins. J Cell Biol 179(5):881-93
14) Chan NC and Lithgow T  (2008) The peripheral membrane subunits of the SAM complex function codependently in mitochondrial outer membrane biogenesis. Mol Biol Cell 19(1):126-36