4.3. The third dsRBD of Xlrbpa (xl3) is a protein/protein dimerization domain
The strongest interacting partner from a two-hybrid screen with Xlrbpa turned out to be Xlrbpa itself. Two-hybrid assays with deletion constructs together with coimmunoprecipitation experiments identified xl3 but neither xl1 nor xl2 as a dimerization domain (Fig. 18, 19 and 20). Xl3 enhances the PKR antagonistic ability of Xlrbpa as previously indicated and discussed. The third domains of PACT and RAX, the human and mouse homologues of Xlrbpa, are the most homologous to the third domain of Xlrbpa (Ito et al., 1999; Patel et al., 2000; Patel and Sen, 1998; Peters et al., 2001). In this work we show that PACT can dimerize with xl3. This fact and the high degree of homology between the third domain of PACT and xl3, are a strong indication that PACT is also …show more content…
The sequences shown above are the best hits from a BLAST search with (xl3). prbp3: third dsRBD of protamine binding protein, trbp3: third dsRBD of TAR-RNA binding protein, Dros: a dsRBD from a Drosophila protein of unknown function. DMStau, a type B dsRBD from Drosophila Staufen protein
4.4. Different activities between Xlrbpa and PACT
In this work we could show that Xlrbpa inhibits human PKR in Saccharomyces cerevisiae cells and that this inhibition is due to the RNA binding-ability of Xlrbpa. Others have cloned the human homologue of Xlrbpa, PACT from a two-hybrid screen with PKR. Experiments in Saccharomyces cerevisiae indicate that PACT is an activator of PKR (Patel and Sen, 1998). The mouse homologue of PACT was cloned as well and also turned out to be a PKR activator (Ito et al., 1999). These results seem to be in contradiction with our results and with experiments done on TRBP (a human protein that is highly similar to PACT, RAX and Xlrbpa) which is a PKR inhibitor (Benkirane et al., 1997; Cosentino et al., 1995; Daher et al., 2001; Park et al., 1994). To test if
The strongest interacting partner from a two-hybrid screen with Xlrbpa turned out to be Xlrbpa itself. Two-hybrid assays with deletion constructs together with coimmunoprecipitation experiments identified xl3 but neither xl1 nor xl2 as a dimerization domain (Fig. 18, 19 and 20). Xl3 enhances the PKR antagonistic ability of Xlrbpa as previously indicated and discussed. The third domains of PACT and RAX, the human and mouse homologues of Xlrbpa, are the most homologous to the third domain of Xlrbpa (Ito et al., 1999; Patel et al., 2000; Patel and Sen, 1998; Peters et al., 2001). In this work we show that PACT can dimerize with xl3. This fact and the high degree of homology between the third domain of PACT and xl3, are a strong indication that PACT is also …show more content…
The sequences shown above are the best hits from a BLAST search with (xl3). prbp3: third dsRBD of protamine binding protein, trbp3: third dsRBD of TAR-RNA binding protein, Dros: a dsRBD from a Drosophila protein of unknown function. DMStau, a type B dsRBD from Drosophila Staufen protein
4.4. Different activities between Xlrbpa and PACT
In this work we could show that Xlrbpa inhibits human PKR in Saccharomyces cerevisiae cells and that this inhibition is due to the RNA binding-ability of Xlrbpa. Others have cloned the human homologue of Xlrbpa, PACT from a two-hybrid screen with PKR. Experiments in Saccharomyces cerevisiae indicate that PACT is an activator of PKR (Patel and Sen, 1998). The mouse homologue of PACT was cloned as well and also turned out to be a PKR activator (Ito et al., 1999). These results seem to be in contradiction with our results and with experiments done on TRBP (a human protein that is highly similar to PACT, RAX and Xlrbpa) which is a PKR inhibitor (Benkirane et al., 1997; Cosentino et al., 1995; Daher et al., 2001; Park et al., 1994). To test if