De novo synthesis of peroxisomes upon mitochondrial targeting of Pex3p.

Peroxisomes can form either by growth and division of pre-existing peroxisomes or by de novo synthesis from the endoplasmic reticulum. Pex3p is the key component for both pathways and its targeting to the ER is thought to initiate the de novo formation of peroxisomes. Here, we addressed the question whether Pex3p also can induce peroxisome formation from mitochondrial membranes.

Cotranslational assembly of the yeast SET1C histone methyltransferase complex.

While probing the role of RNA for the function of SET1C/COMPASS histone methyltransferase, we identified SET1RC (SET1 mRNA-associated complex), a complex that contains SET1 mRNA and Set1, Swd1, Spp1 and Shg1, four of the eight polypeptides that constitute SET1C. Characterization of SET1RC showed that SET1 mRNA binding did not require associated Swd1, Spp1 and Shg1 proteins or RNA recognition motifs present in Set1. RNA binding was not observed when Set1 protein and SET1 mRNA were derived from independent genes or when SET1 transcripts were restricted to the nucleus.

Farnesylation of pex19p is required for its structural integrity and function in peroxisome biogenesis.

The conserved CaaX box peroxin Pex19p is known to be modified by farnesylation. The possible involvement of this lipid modification in peroxisome biogenesis, the degree to which Pex19p is farnesylated, and its molecular function are unknown or controversial. We resolve these issues by first showing that the complete pool of Pex19p is processed by farnesyltransferase in vivo and that this modification is independent of peroxisome induction or the Pex19p membrane anchor Pex3p.

The N-domain of Pex22p can functionally replace the Pex3p N-domain in targeting and peroxisome formation.

Pex3p is a central component of the import machinery for peroxisomal membrane proteins (PMPs) that can reach peroxisomes via the endoplasmic reticulum (ER) and even trigger de novo peroxisome formation from the ER. Pex19p is the import receptor for type I PMPs, whereas targeting of type II PMPs, of which Pex3p so far represents the only species, does not require Pex19p. Pex3p possesses two domains with distinct function: a short N-terminal domain, which harbors the information for peroxisomal (and ER) targeting, and a C-terminal domain, which faces the cytosol and serves as a docking site for Pex19p, thereby delivering newly synthesized PMPs to the peroxisome.

Conservation of PEX19-binding motifs required for protein targeting to mammalian peroxisomal and trypanosome glycosomal membranes.

Glycosomes are divergent peroxisomes found in trypanosomatid protozoa, including those that cause severe human diseases throughout much of the world. While peroxisomes are dispensable for both yeast (Saccharomyces cerevisiae and others) and mammalian cells in vitro, glycosomes are essential for trypanosomes and hence are viewed as a potential drug target. The import of proteins into the matrix of peroxisomes utilizes multiple peroxisomal membrane proteins which require the peroxin PEX19 for insertion into the peroxisomal membrane.

Targeting of the tail-anchored peroxisomal membrane proteins PEX26 and PEX15 occurs through C-terminal PEX19-binding sites.

Tail-anchored proteins contain a single transmembrane domain (TMD) followed by a short C-terminal domain extending into the organellar lumen. Tail-anchored proteins are thought to target to the correct subcellular compartment by virtue of general physicochemical properties of their C-termini; however, the machineries that enable correct sorting remain largely elusive. Here we analyzed targeting of the human peroxisomal tail-anchored protein PEX26.

Function of the PEX19-binding site of human adrenoleukodystrophy protein as targeting motif in man and yeast. PMP targeting is evolutionarily conserved.

We predicted in human peroxisomal membrane proteins (PMPs) the binding sites for PEX19, a key player in the topogenesis of PMPs, by virtue of an algorithm developed for yeast PMPs. The best scoring PEX19-binding site was found in the adrenoleukodystrophy protein (ALDP). The identified site was indeed bound by human PEX19 and was also recognized by the orthologous yeast PEX19 protein.