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- Inturi, Raviteja, 1985-, et al.
(författare)
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A splice variant of the human phosphohistidine phosphatase 1 (PHPT1) is degraded by the proteasome
- 2014
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Ingår i: International Journal of Biochemistry and Cell Biology. - : Elsevier. - 1357-2725 .- 1878-5875. ; 57, s. 69-75
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Tidskriftsartikel (refereegranskat)abstract
- Regulation of protein activity by phosphorylation is central in many cellular processes. Phosphorylation of serine, threonine and tyrosine residues is well documented and studied. In addition, other amino acids, like histidine can be phosphorylated, but neither the mechanism nor the function of this modification is well understood. Nevertheless, there is a 14 kDa enzyme with phosphohistidine phosphatase activity, named PHPT1, found in most animals, but not in bacteria, plant or fungi. There are a few splice variant transcripts formed from the human PHPT1 locus and some of them are predicted to form variant proteins, but studies of these proteins are lacking. In order to get insight into the possible function of the variant transcripts encoded at the PHPT1 locus, ectopic expression of PHPT1 transcript variant 6, predicted to be degraded by the non-sense mediated mRNA decay pathway, in HeLa cells was undertaken. In HeLa cells the splice variant protein was degraded by the proteasome, unlike the wild type protein. Using an in silico modeling approach the variant C-terminal end of the proteins were predicted to form different secondary structures that might explain the different properties of the two proteins. The specific degradation of the PHPT1 splice variant indicates that at least for the PHPT1 protein, the quality control and the self-guarding of the cellular system works at two levels, first at the RNA level, aberrant transcripts are degraded by the non-sense mediated mRNA decay pathway, and the small amount of proteins that are formed will be degraded by the proteasome.
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| 2. |
- Steinhauf, Daniel, et al.
(författare)
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Silencing Motifs in the Clr2 Protein from Fission Yeast, Schizosaccharomyces pombe
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:1, s. e86948-
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Tidskriftsartikel (refereegranskat)abstract
- The fission yeast, Schizosaccharomyces pombe, is a well-established model for heterochromatin formation, but the exact sequence of events for initiation remains to be elucidated. The essential factors involved include RNA transcribed from repeated sequences together with the methyltransferase Clr4. In addition, histone deacetylases, like Clr3, found in the SHREC complex are also necessary for transcriptional silencing. Clr2 is another crucial factor required for heterochromatin formation found in the SHREC complex. The function of Clr2 has been difficult to establish due to the lack of conserved domains or homology to proteins of known molecular function. Using a bioinformatics approach, three conserved motifs in Clr2 were identified, which contained amino acids important for transcriptional repression. Analysis of clr2 mutant strains revealed a major role for Clr2 in mating-type and rDNA silencing, and weaker effects on centromeric silencing. The effect on mating-type silencing showed variegation in several of the strains with mutated versions of Clr2 indicating an establishment or maintenance defect. Moreover, the critical amino acids in Clr2 were also necessary for transcriptional repression in a minimal system, by the tethering of Clr4 upstream of a reporter gene, inserted into the euchromatic part of the genome. Finally, in silico modeling suggested that the mutations in Clr2 cause disruption of secondary structures in the Clr2 protein. Identification of these critical amino acids in the protein provides a useful tool to explore the molecular mechanism behind the role of Clr2 in heterochromatin formation.
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