Peroxisome biogenesis: advances and conundrums.

Investigations of peroxisome biogenesis in diverse organisms reveal new details of this unique process and its evolutionary conservation. Interactions among soluble receptors and the membrane peroxins that catalyze protein translocation are being mapped. Ubiquitination is observed. A receptor enters the organelle carrying folded cargo and recycles back to the cytosol. Tiny peroxisome remnants - vesicles and tubules - are discovered in pex3 mutants that lack the organelle. When the mutant is transfected with a good PEX3 gene, these protoperoxisomes acquire additional membrane peroxins and then import the matrix enzymes to reform peroxisomes. Thus, de novo formation need not be postulated. Dynamic imaging of yeast reveals dynamin-dependent peroxisome division and regulated actin-dependent segregation of the organelle before cell division. These results are consistent with biogenesis by growth and division of pre-existing peroxisomes.