Operons

Operons (clusters of co-regulated genes with related functions) are common features of bacterial genomes. More recently, functional gene clustering has been reported in eukaryotes, from yeasts to filamentous fungi, plants, and animals. Gene clusters can consist of paralogous genes that have most likely arisen by gene duplication. However, there are now many examples of eukaryotic gene clusters that contain functionally related but non-homologous genes and that represent functional gene organizations with operon-like features (physical clustering and co-regulation). These include gene clusters for use of different carbon and nitrogen sources in yeasts, for production of antibiotics, toxins, and virulence determinants in filamentous fungi, for production of defense compounds in plants, and for innate and adaptive immunity in animals (the major histocompatibility locus). The aim of this article is to review features of functional gene clusters in prokaryotes and eukaryotes and the significance of clustering for effective function

Fishing for iron: the effects of salmon on non-haem iron absorption

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The glyoxylate cycle in Ostertagia (Teladorsagia) circumcincta

Ostertagia (Teladorsagia) circumcincta is a nematode parasite which infects the abomasum of sheep and goats. The utilisation of substrates for energy production in O. circumcincta is largely unknown. This parasite has been shown to consume oxygen, and have a full glycolytic and TCA cycle in both L3 and adult stages, although the metabolism of carbohydrates in adults appears to be more geared towards an anaerobic pathway. As well as glycogen, O. circumcincta also contains high levels of stored lipid in both L3 and adult stages, which could also be utilised to provide energy. However, the relative importance of glycogen and lipid for energy production is unknown: in the L3, in which nutrient intake is thought to be restricted by the presence of the sheath; or the adult, in which lipid metabolism may be restricted by oxygen supply. The key enzymes of the glyoxylate cycle, malate synthase and isocitrate would allow this parasite to convert lipid to glucose for metabolism via glycolysis. The enzyme phosphoenolpyruvate carboxykinase (PEPCK) has also been detected in both L3 and adult O. circumcincta. Although this enzyme is typically associated with anaerobic metabolism in nematode parasites, it is also central to gluconeogenesis. As the O. circumcincta has a full TCA cycle and consumes oxygen, gluconeogenesis may be the key function of PEPCK in this parasite species, particularly in L3s. The activity of the glyoxylate cycle along relative levels of glycogen and lipid in L3 and adults of different ages will be discussed