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Gene Review

SMI1  -  Smi1p

Saccharomyces cerevisiae S288c

Synonyms: Cell wall assembly regulator SMI1, G8553, KNR4, KTR4, Killer toxin-resistance protein 4, ...
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High impact information on SMI1

  • We cloned and sequenced the SMI1 gene, which encodes a 57-kDa polypeptide with evolutionarily conserved epitope(s) found in mammalian cell nuclei [1].
  • Another mutant (smi1) exhibited a rare phenotype at the nonpermissive condition, which included S phase and budding arrest [1].
  • Disruption of the KNR4 locus does not result in cell death; however, it leads to reduced levels of both (1,3)-beta-glucan synthase activity and (1,3)-beta-glucan content in the cell wall [2].
  • In this paper, we demonstrate by two-hybrid, in vitro immunoprecipitation and tandem affinity purification (TAP) methods that Knr4p physically interacts with Slt2p [3].
  • KNR4, a suppressor of Saccharomyces cerevisiae cwh mutants, is involved in the transcriptional control of chitin synthase genes [4].

Biological context of SMI1

  • The KNR4 gene, originally isolated by complementation of a K9 killer-toxin-resistant mutant displaying reduced levels of both 1,3-beta-glucan and 1,3-beta-glucan synthase activity, was recloned from a YCp50 genomic library as a suppressor of Saccharomyces cerevisiae calcofluor-white-hypersensitive (cwh) mutants [4].
  • In addition, it is shown that the efficiency of spores formation was drastically reduced in diploid cells homozygous for the disruption of KNR4 or for a temperature-sensitive mutation of TYS1, although this effect could be independent of their protein interaction [5].
  • Moreover, the replacement of the two in vivo phosphorylated Ser(200) and Ser(203) by alanines led to a mutated protein with reduced protein interactions and a weaker complementation ability towards knr4 null mutant phenotypes [6].
  • These results together with previous data from genome scale two-hybrid and synthetic interaction screens support the notion that Knr4 is a regulatory protein that participates in the coordination of cell wall synthesis with bud emergence, and that this function may be modulated by phosphorylation of this protein [6].
  • Furthermore, the cell wall biogenesis protein KNR4 which physically interacts with TyrRS and cooperates in beta-1,3 glucan biosynthesis falls into a single gene cluster with TyrRS [7].

Anatomical context of SMI1


Associations of SMI1 with chemical compounds

  • In these mutants, which were characterized by increased chitin levels, the suppressor effect of KNR4 resulted, for some of them, in a lowering of polymer content to close to wild-type level, with no effect on the contents of beta-glucan and mannan [4].
  • Interaction of Knr4 protein, a protein involved in cell wall synthesis, with tyrosine tRNA synthetase encoded by TYS1 in Saccharomyces cerevisiae [5].
  • In exponentially growing cells on glucose, Knr4 appeared to be present in a protein complex that migrates with an apparent Mw superior to 250 kDa [6].

Other interactions of SMI1

  • Overexpression of either of the two genes in a wild-type strain led to increased resistance to wall-affecting drugs, while this effect was not obtained in a bck2 Delta mutant that overexpressed KNR4 [8].


  1. Yeast calmodulin and a conserved nuclear protein participate in the in vivo binding of a matrix association region. Fishel, B.R., Sperry, A.O., Garrard, W.T. Proc. Natl. Acad. Sci. U.S.A. (1993) [Pubmed]
  2. Cloning and characterization of KNR4, a yeast gene involved in (1,3)-beta-glucan synthesis. Hong, Z., Mann, P., Brown, N.H., Tran, L.E., Shaw, K.J., Hare, R.S., DiDomenico, B. Mol. Cell. Biol. (1994) [Pubmed]
  3. The interaction of Slt2 MAP kinase with Knr4 is necessary for signalling through the cell wall integrity pathway in Saccharomyces cerevisiae. Martin-Yken, H., Dagkessamanskaia, A., Basmaji, F., Lagorce, A., Francois, J. Mol. Microbiol. (2003) [Pubmed]
  4. KNR4, a suppressor of Saccharomyces cerevisiae cwh mutants, is involved in the transcriptional control of chitin synthase genes. Martin, H., Dagkessamanskaia, A., Satchanska, G., Dallies, N., François, J. Microbiology (Reading, Engl.) (1999) [Pubmed]
  5. Interaction of Knr4 protein, a protein involved in cell wall synthesis, with tyrosine tRNA synthetase encoded by TYS1 in Saccharomyces cerevisiae. Dagkessamanskaia, A., Martin-Yken, H., Basmaji, F., Briza, P., Francois, J. FEMS Microbiol. Lett. (2001) [Pubmed]
  6. The 'interactome' of the Knr4/Smi1, a protein implicated in coordinating cell wall synthesis with bud emergence in Saccharomyces cerevisiae. Basmaji, F., Martin-Yken, H., Durand, F., Dagkessamanskaia, A., Pichereaux, C., Rossignol, M., Francois, J. Mol. Genet. Genomics (2006) [Pubmed]
  7. Bioinformatic analysis of changes in expression level of tyrosyl-tRNA synthetase during sporulation process in Saccharomyces cerevisiae. Ivakhno, S.S., Kornelyuk, A.I. Mikrobiol. Z. (2005) [Pubmed]
  8. KNR4 is a member of the PKC1 signalling pathway and genetically interacts with BCK2, a gene involved in cell cycle progression in Saccharomyces cerevisiae. Martin-Yken, H., Dagkessamanskaia, A., Talibi, D., Francois, J. Curr. Genet. (2002) [Pubmed]
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