InterPro domain: IPR018958

This domain is found in the yeast cell wall assembly regulator Smi1 (also known as Knr4) [ 1 , 2 ].

Saccharomyces cerevisiae Knr4 has a regulatory role in chitin deposition and in cell wall assembly [ 3 ]. It is believed to connect the PKC1-SLT2 MAPK pathway with cell proliferation. It has been shown to interact with Bck2, a gene involved in cell cycle progression in S. cerevisiae (forming a complex) to allow PKC1 to coordinate the cell cycle (cell proliferation) with cell wall integrity [ 4 , 5 ]. Knr4 also interacts with the tyrosine-tRNA synthetase protein encoded by Tys1 and is involved in sporulation process [ 6 ].

Proteins containing this domain also include the animal F-box only protein 3 (FBXO3). In humans, FBXO3 is a substrate recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex [ 7 ].

Interestingly, Smi1/Knr4 homologues from bacteria are potential immunity proteins in a subset of these contact-dependent inhibitory toxin systems [ 8 ].

Note: previously reported evidence that Knr4 may interact with nuclear matrix-association region [ 9 ] may be due to an artefact [ 10 ].

1. Cloning and characterization of a Neurospora crassa gene required for (1,3) beta-glucan synthase activity and cell wall formation. Proc. Natl. Acad. Sci. U.S.A. 91, 9500-4
2. Cloning and characterization of KNR4, a yeast gene involved in (1,3)-beta-glucan synthesis. Mol. Cell. Biol. 14, 1017-25
3. KNR4, a suppressor of Saccharomyces cerevisiae cwh mutants, is involved in the transcriptional control of chitin synthase genes. Microbiology (Reading, Engl.) 145 ( Pt 1), 249-58
4. KNR4 is a member of the PKC1 signalling pathway and genetically interacts with BCK2, a gene involved in cell cycle progression in Saccharomyces cerevisiae. Curr. Genet. 41, 323-32
5. The interaction of Slt2 MAP kinase with Knr4 is necessary for signalling through the cell wall integrity pathway in Saccharomyces cerevisiae. Mol. Microbiol. 49, 23-35
6. Interaction of Knr4 protein, a protein involved in cell wall synthesis, with tyrosine tRNA synthetase encoded by TYS1 in Saccharomyces cerevisiae. FEMS Microbiol. Lett. 200, 53-8
7. PML activates transcription by protecting HIPK2 and p300 from SCFFbx3-mediated degradation. Mol. Cell. Biol. 28, 7126-38
8. A novel immunity system for bacterial nucleic acid degrading toxins and its recruitment in various eukaryotic and DNA viral systems. Nucleic Acids Res. 39, 4532-52
9. Yeast calmodulin and a conserved nuclear protein participate in the in vivo binding of a matrix association region. Proc. Natl. Acad. Sci. U.S.A. 90, 5623-7