The mammalian endoplasmic reticulum (ER) harbors disulfide bond-generating enzymes, including Ero1α and peroxiredoxin 4 (Prx4), and nearly 20 members of the protein disulfide isomerase family (PDIs), which together constitute a suitable environment for oxidative protein folding. Here, we clarified the Prx4 preferential recognition of two PDI family proteins, P5 and ERp46, and the mode of interaction between Prx4 and P5 thioredoxin domain. Detailed analyses of oxidative folding catalyzed by the reconstituted Prx4–PDIs pathways demonstrated that, while P5 and ERp46 are dedicated to rapid, but promiscuous, disulfide introduction, PDI is an efficient proofreader of non-native disulfides. Remarkably, the Prx4-dependent formation of native disulfide bonds was accelerated when PDI was combined with ERp46 or P5, suggesting that PDIs work synergistically to increase the rate and fidelity of oxidative protein folding. Thus, the mammalian ER seems to contain highly systematized oxidative networks for the efficient production of large quantities of secretory proteins.

Background: In many respects Archaea are much more like eukaryotes than prokaryotes with respect to the conservation of many of the components involved in transcription, translation and DNA replication. So far, only a few DNA polymerases with structures similar to those of eukaryotic DNA polymerase a have been found in Archaea. The identification and characterization of all the DNA polymerases of one archaeon would add considerably to our knowledge of the basic mechanisms of DNA replication in these organisms.

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The curimatã-pacu Prochilodus argenteus is an important characiform from the São Francisco River basin that performs longdistance migrations for spawning upstream during the rainy season, when the temperature and photoperiod are elevated. Despite the interruption of the migratory routes by the Três Marias Dam and accentuated decline in fishing, the curimatã-pacu still sustains the fisheries at the Três Marias region in recent decades. The objective of this study was to evaluate the reproductive activity of P. argenteus in two sections of the São Francisco River, downstream from the Três Marias Dam, during the rainy season. In the first 34 km of the river, immediately below the dam, most of the females were in gonadal resting. At 34-54 km downstream from the dam, following the confluence with a medium-sized tributary, the Abaeté River, there was a high frequency of males and females in reproductive activity. Follicular atresia was more frequent in the upper section of the river while postovulatory follicles occurred predominantly in the lower section. Fulton's condition factor and gonadosomatic index indicated that the females were in a better physiological and reproductive condition below the confluence with the Abaeté River. In contrast to the females, the males were less affected by damming, and testicular maturation was largely achieved in two river sections. Thus, although the section of the São Francisco River immediately below the Três Marias Dam was found to be unfavourable for the reproduction of the migratory fishes due principally to the hypolimnetic water from the reservoir, reproductive success of P. argenteus was achieved below the Abaeté River. In this section, the species encountered appropriate conditions for maturation and spawning, i.e. warm temperatures above 24 C, high water flow and dissolved oxygen, and low water transparency. These results indicate the importance of a non-regulated tributary to minimize the ecological impact of a dam on the downstream native fish communities.

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The silver cat¢sh, Rhamdia quelen, is endemic to North, Central and South America with high aquaculture potential and wide acceptance in the market. Breeder ¢sh were subjected to induced reproduction through hypophysation using a crude common carp pituitary extract. Egg characteristics, oocyte surface ultrastructure and histology of larval ontogenesis until whole yolk resorption were described for the ¢rst time for this species. Oocytes and semen were obtained by manual extrusion, and fertilization was conducted using the dry method. After fertilization, eggs were kept in incubators at 24 1C. The embryonic development was monitored using a stereomicroscope every 10 min until hatching. To analyse the larval development, larvae samples were collected from incubators daily until the ¢fth day, ¢xed in Bouin's £uid and subjected to routine histological techniques. The oocyte extrusion occurred 8 h after the second hormone dose at 26 1C. The oocytes were spherical, non-adhesive and yellow, with a diameter of 1471.75 AE 47.63 mm. Scanning electron microscopy revealed a thin jelly coat covering the zona radiata in the animal pole around the micropyle. The blastopore closure occurred within 8 h after fertilization, and the fertilization rate was 79.9 AE 5.2% at 24 1C. Embryonic development was completed within 25 h 30 min after fertilization. The complete resorption of the yolk and the formation of the digestive system organs and the mouth opening occurred on the ¢fth day, indicating a need for exogen-ous feeding. The results of this study provide information important for improvement in R. quelen culture and management. Early development of silver cat¢sh M P deAmorim et al. Early development of silver cat¢sh M P deAmorim et al.

Almost all organisms, from bacteria to humans, possess catalytic systems that promote disulfide bond formation-coupled protein folding, i.e. oxidative protein folding. These systems are necessary for the biosynthesis of many secretory and membrane proteins, such as antibodies, major histocompatibility complex molecules, growth factors, and insulin. Over the last decade, structural studies have made striking progress in this field of research, identifying how oxidative systems operate in a specific and regulated manner to maintain redox and protein homeostasis within cells. Interestingly, more and more novel catalysts that promote disulfide bond formation have been discovered in mammals, suggesting that the oxidative protein folding network is even more complicated in higher eukaryotes than previously thought. This review highlights the physiological roles and molecular bases of the disulfide bond formation pathways that have evolved in the bacterial periplasm and the endoplasmic reticulum of fungi and mammals. Accumulating knowledge about disulfide bond formation networks widely distributed throughout the biological kingdom has significantly advanced our understanding of the cellular mechanisms dedicated to protein quality control.