Elongation of the cytoplasmic tail interferes with the fusion activity of influenza virus hemagglutinin

The hemagglutinin (HA) of fowl plague virus was lengthened and shortened by site-specific mutagenesis at the cytoplasmic tail, and the effects of these modifications on HA functions were analyzed after expression from a simian virus 40 vector. Elongation of the tail by the addition of one to six histidine (His) residues did not interfere with intracellular transport, glycosylation, proteolytic cleavage, acylation, cell surface expression, and hemadsorption. However, the ability to induce syncytia at a low pH decreased dramatically depending on the number of His residues added. Partial fusion (hemifusion), assayed by fluorescence transfer from octadecylrhodamine-labeled erythrocyte membranes, was also reduced, but even with the mutant carrying six His residues, significant transfer was observed. However, when the formation of fusion pores was examined with hydrophilic fluorescent calcein, transfer from erythrocytes to HA-expressing cells was not observed with the mutant carrying six histidine residues. The addition of different amino acids to the cytoplasmic tail of HA caused an inhibitory effect similar to that caused by the addition of His. On the other hand, a mutant lacking the cytoplasmic tail was still able to fuse at a reduced level. These results demonstrate that elongation of the cytoplasmic tail interferes with the formation and enlargement of fusion pores. Thus, the length of the cytoplasmic tail plays a critical role in the fusion process.     

Effect of testosterone on long-term organ cultures of canine prostate

Organ cultures of rodent and human prostate glands have shown marked differences in their morphological response to testosterone. In this study, explants from 19 canine prostate glands were cultivated for a minimum of 9 days in Trowell's T-8 medium. Groups of explants were exposed to media containing from 0.05 to 100 mum testosterone. While the higher testosterone levels (50 and 100 mum) markedly decreased explant viability, explants cultivated at lower levels (0.05 to 5 mum) appeared similar to control explants in testosterone-free Trowell's T-8 medium. Atmospheric mixtures containing either 95% or 50% oxygen were equally effective. Shortly after the cultures were initiated, large amounts of secretory product were liberated into the lumen. After 9 or more days in vitro, glandular epithelium appeared cuboidal and never revealed the acid phosphatase-rich secretory granules seen in the preculture control. However, the epithelium exhibited an increase in alkaline phosphatase and lipid content following cultivation.     

Species‐specific fish larvae drift in anthropogenically constructed riparian zones on the Vienna impoundment of the River Danube,Austria: Species occurrence,frequencies, and seasonal patterns based on DNA barcoding

As a result of river regulations over several centuries, followed by restoration measures in recent decades, most of the River Danube shoreline is man‐made, primarily riprap, but some reconstructed gravel banks and riparian side arms. We investigated the effects of these different structures on fish larval dispersal over a 20‐km stretch in Vienna via the use of drift nets. The habitats examined were created 18 years ago when the impoundment of the Danube hydropower station Vienna/Freudenau was constructed. About 15,000 fish larvae were trapped, and a subsample was determined to species level by DNA barcoding. In total, 26 different species were detected, including 10 species that are endangered or in danger of extinction. When species composition was considered, cyprinids become dominant at sites downstream of gravel bars, whereas in riprap sections, the majority of the larvae consist of invasive Gobiidae. Side arm habitats provide spawning and nursery grounds for additional species. Furthermore, clear species‐related seasonal patterns were observed with peak densities and multiple spawning periods of some species being recorded. The largest peak of Percidae occurred in the first half of May, followed by Cyprinidae at the end of May and Gobiidae in mid‐June.     

An efficient solution technique for discrete-time queues fed by heterogeneous traffic

During the past couple of years, a lot of effort has been put into solving all kinds of Markov modulated discrete-time queueing models, which occur, almost in a natural way, in the performance analysis of slotted systems, such as asynchronous transfer mode (ATM) multiplexers and switching elements. However, in most cases, the practical application of such solutions is limited, because of the large state space that is usually involved. In this paper we try to take a first step towards obtaining approximate solutions for a discrete-time multiserver queueing model with a general heterogeneous Markove modulated cell arrival process, which allows accurate predictions concerning the behaviour of the buffer occupancy in such a model and still remains tractable, both from an analytical and a computational point of view. We first introduce a solution technique which leads to a closed-form expression for the joint probability generating function of the buffer occupancy and the state of the arrival process, from which an expression for V(z), the probability generating function of the buffer occupancy is easily derived. On the basis of this result we propose an approximation for the boundary probabilities, which reduces all calculations to an absolute minimum. In addition, we show how accurate data for the distribution of the buffer occupancy can be obtained, by using multiple poles of V(z) in the geometric-tail approximation of the distribution. ©1997 by John Wiley & Sons, Ltd.     

Skin-core structure and bimodal Weibull distribution of the strength of carbon fibers

The bimodal Weibull parameters of polyacrylonitrile-based carbon fibers were obtained from the fiber-bundle tension test. The bimodality increases with increasing high temperature treatment up to 2100 °C and then decreases for the highest temperature treatment of 2400 °C. The local structure of the fibers was investigated by scanning X-ray microdiffraction using synchrotron radiation. This enables the mapping of the atomistic structure across the fiber with a position resolution of 100 nm. The mechanical bimodality is attributed to a reversal of the observed skin structure from less orientation to higher orientation as compared to the core.