Matchmaking for Chromosomes

HIGHLIGHTS

WEB WATCH CELL DIVISION

Passionate about peroxisomes Peroxisomes are spherical Matchmaking for organelles that compartmentalize many metabolic reactions. If this chromosomes introduction doesn’t sound overly appealing, go to the peroxisome website — The oscillation of an organism together only at the onset of meiotic created and maintained in between haploid and diploid stages is prophase in diploids, polyploids pair Stephen J. Gould’s laboratory the very essence of sexual reproduc- their chromosomes long before — and you’ll develop a deep tion. Thus the ability to accurately pair meiosis begins. love for these organelles. The site is unique in that the and separate homologous chromo- In 1958, the agricultural geneticist information is pitched at somes during meiosis is essential for Sir Ralph Riley identified the PH1 three levels: scientist, any sexually reproducing organism. locus in wheat to be essential for cor- physician or layperson. The Reporting in Nature, Graham Moore rect homologous chromosome pair- scientist will find a and colleagues at the John Innes ing and recombination. As a result of comprehensive and up-to- Centre, Norwich, UK, have explored his work, a single mutant carrying a date review of peroxisome how this fidelity is maintained. deletion of this locus has been used in biology, whereas the physician’s version focuses Pairing of homologous chromo- wheat breeding ever since. Its activity on peroxisomal disorders. somes is difficult enough in a diploid has remained controversial, however, And your hypochondriac organism, but many plants are poly- and even its composition is unclear. but in the absence of the PH1 locus grandfather will be able to ploid with, in effect, several genomes Moore and colleagues used confo- there were more centromere pairs surf the layperson’s version, sharing each cell. Pairing of chromo- cal microscopy to investigate PH1 and fewer singlets than in its pres- and discover all sorts of somes occurs mainly through the function after the pairing of chromo- ence. In wheat/rye hybrid plants, the peroxisome-related diseases that he might have. centromeres, so in wheat, a hexa- somes in developing xylem cells from chromosomes from the different par- In the scientist’s version, ploid, each centromere has five very wheat. They were particularly con- ents could be identified, allowing the after the first page of similar potential partners, only one cerned with a stage at the beginning authors to deduce that there was less introduction, you can go in of which is its true homologue. One of meiosis when a ‘telomere bouquet’ mispairing of centromeres in the two directions: peroxisome might expect that this complexity forms. Here, all of the telomeres (red presence of PH1. biogenesis or biochemistry of would result in meiosis taking longer in the figure) come together at one The molecular mechanism by the peroxisome. The two directions then zoom in on in polyploid species compared with side of the dividing cell, whereas the which the PH1 locus weeds out individual molecule pages or diploids — but in fact it is faster. centromeres (green) congregate at incorrect centromere pairings before enzymatic reaction pages, This is probably because, while the other. It was difficult to distin- meiosis begins — so that only correct respectively. The molecule homologous chromosomes come guish paired from single centromeres, pairings are carried into cell division pages are short summaries about the different peroxins, with a comprehensive bibliography. There are also TRANSLOCATION chimaeras consisting of a PTS2 partly protected from protease links to sidetrack pages that signal sequence, a prethiolase- digestion, indicating that it was no comment on controversies in longer inside the peroxisome but the field. The only possible processing site, a FLAG epitope and concern about the site is that, Paradigm lost Pex5. The FLAG epitope can be had docked again to the organelle as it is the creation of a single detected by two antibodies: M2, membrane. Last, kinetic data laboratory, these comments which recognizes it in any context; indicated that processed Pex5 might carry some bias. The accepted model for protein and M1, which recognizes it only could re-enter peroxisomes, as the The site has no fancy web import into organelles is that when it is amino terminal — as, for appearance of the peroxisomal, stuff — the cartoons are targeting is mediated by receptors example, after cleavage of the processed form accounted for the simple, and there are no that recognize signal sequences. construct by the prethiolase disappearance of the processed and animations or flashing protease. Because the protease unprocessed forms from the headers — but the graphics, Once cargo proteins have reached cytosol. although simple, are pleasant the correct membrane, they cleaves prethiolase only in the to look at. More importantly, unfold, thread through the peroxisome matrix, cleavage of the So peroxisomal import seems to be the information is beautifully translocon and refold in the lumen construct is diagnostic of entry diametrically opposed to the organized. Peroxisomes are of the organelle. Of course, into peroxisomes. principles derived from import into far less well understood than nothing is ever simple, and After expression in HeLa cells, the mitochondria.Although it remains other organelles, so the Dammai and Subramani now chimaera was cleaved, indicating to be shown that cycling of Pex5 amount of information is not report in Cell that Pex5 — the that Pex5 had entered peroxisomes. between the cytosol and the yet overwhelming. But the receptor for the peroxisomal Pex5 was also exported from peroxisome is relevant for cargo creators of this site have targeting signal 1 — actually cycles peroxisomes, as the processed form transport, this shuttling mechanism demonstrated here what you was largely cytosolic. Peroxisome- is reminiscent of nuclear transport. can do with a bit of time and in and out of peroxisomes. The directionality of nuclear love for your research. The authors constructed associated, processed Pex5 was only Raluca Gagescu