Fairy wrasses perceive and respond to their deep red fluorescent coloration

Fluorescence enables the display of wavelengths that are absent in the natural environment, offering the potential to generate conspicuous colour contrasts. The marine fairy wrasse Cirrhilabrus solorensis displays prominent fluorescence in the deep red range (650–700 nm). This is remarkable because marine fishes are generally assumed to have poor sensitivity in this part of the visual spectrum. Here, we investigated whether C. solorensis males can perceive the fluorescence featured in this species by testing whether the presence or absence of red fluorescence affects male–male interactions under exclusive blue illumination. Given that males respond aggressively towards mirror-image stimuli, we quantified agonistic behaviour against mirrors covered with filters that did or did not absorb long (i.e. red) wavelengths. Males showed significantly fewer agonistic responses when their fluorescent signal was masked, independent of brightness differences. Our results unequivocally show that C. solorensis can see its deep red fluorescent coloration and that this pattern affects male–male interactions. This is the first study to demonstrate that deep red fluorescent body coloration can be perceived and has behavioural significance in a reef fish.     

Sequences required for self-catalysed cleavage of the satellite RNA of tobacco ringspot virus

The satellite RNA of tobacco ringspot virus (sTobRV) undergoes self-catalysed cleavage during replication. A plasmid for in vitro expression of sTobRV has been constructed and used to obtain a library of mutagenized sTobRV sequences. Screening of these mutants has allowed precise definition of the sequences required for (+) and (-) strand cleavage. The sequences and RNA structures associated with cleavage of each strand differ markedly. Cleavage of the (+) strand requires those sequences flanking the site for cleavage to form a 'hammerhead' domain, similar to those found in other satellite and viroid RNA. In contrast, cleavage of the (-) strand requires only a small region of 12 nucleotides (nt) at the site of cleavage, and a sequence of 55 nt positioned elsewhere in the molecule. Comparison with a closely related satellite suggests that a novel RNA structure may be involved in (-) strand cleavage.     

Inactivation of the streptokinase gene prevents Streptococcus equisimilis H46A from acquiring cell-associated plasmin activity in the presence of plasminogen

Abstract The effects of some physico-chemical parameters on production of extracellular α-L-arabinofuranosidase by Aspergillus nidulans were examined. Highest levels of α-L-arabinofuranosidase were generated with cultures grown on 1% (w/v) purified beet pulp arabinan at 30°C and at an initial pH of 7.0. The enzyme was shown to be very sensitive to the action of proteases. Zymogram overlay of a protein profile obtained by SDS-PAGE revealed the occurrence of a band ( M _r 36 000) exhibiting α-L-arabinofuranosidase activity. The isoelectric pH of the enzyme lay near 4.3. Temperature and pH optima for the activity of crude α-L-arabinofuranosidase preparations were 55°C and 5.5, respectively. Enzyme activity was greatly reduced by thiol reagents such as Hg²⁺ and p -hydroxymercuribenzoate and showed a K _m value of 2.7 mM on p -nitrophenyl α-L-arabinofuranoside as substrate.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Immunodominant CD4+ T-cell epitope within nonstructural protein 3 in acute hepatitis C virus infection.

In acute hepatitis C virus infection, 50 to 70% of patients develop chronic disease. Considering the low rate of spontaneous viral clearance during chronic hepatitis C infection, the first few months of interaction between the patient's immune system and the viral population seem to be crucial in determining the outcome of infection. We previously reported the association between a strong and sustained CD4+ T-cell response to nonstructural protein 3 (NS3) of the hepatitis C virus and a self-limited course of acute hepatitis C infection. In this study, we identify an immunodominant CD4+ T-cell epitope (amino acids 1248 to 1261) that was recognized by the majority (14 of 23) of NS3-specific CD4+ T-cell clones from four of five patients with acute hepatitis C infection. This epitope can be presented to CD4+ T cells by HLA-DR4, -DR11, -DR12, -DR13, and -DR16. HLA-binding studies revealed a high binding affinity for 10 of 13 common HLA-DR alleles. Two additional CD4+ T-cell epitopes, amino acids 1388 to 1407 and amino acids 1450 to 1469, showed a very narrow pattern of binding to individual HLA-DR alleles. Our data suggest that the NS3-specific CD4+ T-cell response in acute hepatitis C infection is dominated by a single, promiscuous peptide epitope which could become a promising candidate for the development of a CD4+ T-cell vaccine.