The first steps of ether lipid biosynthesis are exclusively localized to peroxisomes and hence some peroxisomal disorders are characterized by a severe deficiency of plasmalogens, the main ether lipids in humans. Here we report on gene defects of plasmalogen biosynthesis, chromosomal localization of the corresponding genes and, as a consequence of plasmalogen deficiency, on structural alterations of caveolae, clathrin-coated pits, endoplasmic reticulum and Golgi cisternae, as well as on the reduced rate of transferrin receptor cycling. The data suggest that plasmalogens, analogous to cholesterol, are essential for correct membrane functioning and their deficiency results in impaired membrane trafficking.

We report the isolation of 24 novel genotypes of TT viruses from a surgically removed spleen of a patient with Hodgkin's disease. The sequence analysis of our 24 isolates revealed the remarkable heterogeneity of TT virus isolates not only from the same patient but also from the same biopsy material. These isolates belong to four phylogenetic groups of TT viruses. Nucleotide sequence analyses revealed five distinct genotypes (tth3, tth4, tth5, tth6, and tth7). The limited variation in sequence identity of the other isolates defines the latter as variants of four of these genotypes. A group of 6 isolates (the tth7 group) revealed a reorganization of open reading frame 1 (ORF1) leading to one larger and a varying number of smaller ORFs. The nucleotide difference of the full-length genomes was less than 1%. A variation of 69 to 97% in amino acids of a second group of 8 isolates (the tth3 group) was restricted to the hypervariable region of ORF1, indicating the existence of a quasi-species. These isolates differed by less than 2% in the remainder of their nucleotide sequences. An alignment of these isolates with 79 previously reported TT virus genotypes permits the proposal of TT virus genera and species within the family Anelloviridae in analogy to a previous proposal for the papillomaviruses (family Papillomaviridae).TT viruses (TTV) are ubiquitous in nature and have been demonstrated in more than 90% of serum samples from healthy individuals where they persist over time (14,16,27,41). Viral particles have been purified from feces (17, 34) and, in addition, are excreted in saliva, breast milk, and bile juice (9,38,47,49). Transplacental transmission from mother to child has been controversial, but postnatal transmission has been confirmed repeatedly (15,20,24,30,33,37,48,51,52,57 (39,44). Peripheral blood mononuclear cells act as a reservoir for TTV (41), but the highest viral load is found in the granulocytes (54). Viral transcription naturally occurs in bone marrow cells and not in peripheral blood mononuclear cells (40), although transcription in vitro has been achieved by DNA transfection into stimulated peripheral blood monocytes (29) and in a monkey cell line (19).A large number of full-length or near full-length genomes of TTV has been isolated from humans and primates. They have also been identified in farm animals (23), although the genomes of recent isolates from pigs, dogs, and cats proved to be considerably smaller in size than the TTV found in humans and primates (43). The highly conserved noncoding region constitutes about one-third of the genome. The coding region consists of a large open reading frame (ORF), ORF1, coding for the viral capsid protein as well as the smaller ORF2, ORF3, and ORF4. Additional mRNAs result from splicing events (19,40). Many different genotypes have been isolated, and an extremely wide range of DNA sequence divergence has been demonstrated (45). The steadily increasing number of new genotypes and the high sequence variability point to the need for a uniform and defined cla...

In this paper we describe isolation and molecular characterization of human dihydroxyacetonephosphate acyltransferase (DAP-AT). The enzyme was extracted from rabbit Harderian gland peroxisomes and isolated as a trimeric complex by sucrose density gradient centrifugation. From peptide sequences matching EST-clones were obtained which allowed cloning and sequencing of the cDNA from a human cDNA library. The nucleotide-derived amino acid sequence revealed a protein consisting of 680 amino acid residues of molecular mass 77 187 containing a C-terminal type 1 peroxisomal targeting signal. Monospecific antibodies raised against this polypeptide efficiently immunoprecipitated DAP-AT activity from solubilized peroxisomal preparations, thus demonstrating that the cloned cDNA codes for DAP-AT.z 1997 Federation of European Biochemical Societies.

Investigating targeting of the 22 kDa peroxisomal membrane protein (Pmp22p) to the peroxisomal membrane we have confined the targeting signal to amino acid residues 16^37 located in the N-terminal cytoplasmic tail. Comparison of Pmp22p orthologous sequences revealed a conserved motif Y3xL3xP3x(KQN) which might represent the core of this targeting signal not found so far in other Pmps. Fusion of the Pmp22p N-terminal tail to the C-terminal portion of Pmp22p which per se is not targeted to peroxisomes, conveys peroxisomal targeting. These data suggest that Pmp22p is targeted to peroxisomes by a new membrane targeting signal which is necessary and sufficient to target a polypeptide containing two transmembrane spans to peroxisomes.z 2000 Federation of European Biochemical Societies.