Taxonomic distribution of proteins containing YajC domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing YajC domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Protein traffic in bacteria: multiple routes from the ribosome to and across the membrane.

Muller M, Koch HG, Beck K, Schafer U
Prog Nucleic Acid Res Mol Biol. 2001; 66: 107-57

Bacteria use several routes to target their exported proteins to the plasmamembrane. The majority are exported through pores formed by SecY and SecE. Twodifferent molecular machineries are used to target proteins to the SecYEtranslocon. Translocated proteins, synthesized as precursors with cleavablesignal sequences, require cytoplasmic chaperones, such as SecB, to remaincompetent for posttranslational transport. In concert with SecB, SecA targets theprecursors to SecY and energizes their translocation by its ATPase activity. The latter function involves a partial insertion of SecA itself into the SecYEtranslocon, a process that is strongly assisted by a couple of membrane proteins,SecG, SecD, SecF, YajC, and the proton gradient across the membrane. Integralmembrane proteins, however, are specifically recognized by a direct interactionbetween their noncleaved signal anchor sequences and the bacterial signalrecognition particle (SRP) consisting of Ffh and 4.5S RNA. Recognition occursduring synthesis at the ribosome and leads to a cotranslational targeting toSecYE that is mediated by FtsY and the hydrolysis of GTP. No other Sec protein isrequired for integration unless the membrane protein also contains longtranslocated domains that engage the SecA machinery. Discrimination betweenSecA/SecB- and SRP-dependent targeting involves the specificity of SRP forhydrophobic signal anchor sequences and the exclusion of SRP from nascent chains of translocated proteins by trigger factor, a ribosome-associated chaperone. The SecYE pore accepts only unfolded proteins. In contrast, a class of redoxfactor-containing proteins leaves the cell only as completely folded proteins.They are distinguished by a twin arginine motif of their signal sequences that byan unknown mechanism targets them to specific pores. A few membrane proteinsinsert spontaneously into the bacterial plasma membrane without the need fortargeting factors and SecYE. Insertion depends only on hydrophobic interactionsbetween their transmembrane segments and the lipid bilayer and on thetransmembrane potential. Finally, outer membrane proteins of Gram-negativebacteria after having crossed the plasma membrane are released into theperiplasm, where they undergo distinct folding events until they insert astrimers into the outer membrane. These folding processes require distinctmolecular chaperones of the periplasm, such as Skp, SurA, and PpiD.