Figure 1.

TPA formation is specific for Pex11pβ-YFP. Expression of Pex11pβ-YFP in COS-7 cells results in the formation of tubular peroxisomal membrane compartments (TPAs) (A) and inhibits peroxisome division and proliferation normally induced by untagged or Myc-tagged Pex11pβ. These alterations are specific for Pex11pβ-YFP. The expression of N-terminally tagged YFP-Pex11pβ or of Pex11pá-YFP, a homologue of Pex11pβ with similar membrane topology, does not induce TPAs. Interestingly, expression of a Pex11pβ-GFP construct does not induce TPAs (B) indicating that cloning-related differences in the linker region between the Pex11pβ and the (Y)GFP tag might have an effect on protein conformation. Potential oligomerization properties of non-monomeric GFP appear to be less crucial for TPA formation. Although the mechanistic reasons for the inhibitory effect of Pex11pβ-YFP are presently unclear, sterical hindrance during the formation of a functional constriction/division complex and/or some intrinsic “stacking” activity and tight trans-membrane interactions of Pex11pβ-YFP may explain the block in peroxisome division. Nevertheless, the Pex11pβ-YFP fusion protein represents a specific and useful novel tool to further dissect peroxisome proliferation and to investigate early events in peroxisomal growth and division. Bar, 10 µm.