Isolation, DNA sequence, and regulation of a Saccharomyces cerevisiae gene that encodes DNA strand transfer protein alpha.

DNA strand transfer protein alpha (STP alpha) from meiotic Saccharomyces cerevisiae cells promotes homologous pairing of DNA without any nucleotide cofactor in the presence of yeast single-stranded DNA binding protein. This gene (DNA strand transferase 1, DST1) encodes a 309-amino-acid protein with a predicted molecular mass of 34,800 Da. The STP alpha protein level is constant in both mitotic and meiotic cells, but during meiosis the polypeptide is activated by an unknown mechanism, resulting in a large increase in its specific activity. A dst1::URA3/dst1::URA3 mutant grows normally in mitotic media; however, meiotic cells exhibit a greatly reduced induction of both DNA strand transfer activity and intragenic recombination between his1 heteroalleles. Spore viability is normal. These results suggest that DST1 is required for much of the observed induction of homologous recombination in S. cerevisiae during meiosis but not for normal sporulation.     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Structure, Expression and Phylogenetic Analysis of the Gene Encoding Actin I in Pneumocystis Carinii

Actin is a major component of the cytoskeleton and one of the most abundant proteins found in eukaryotic cells. Comparative sequence analysis shows that this essential gene has been highly conserved throughout eukaryotic evolution making it useful for phylogenetic analysis. Complete cDNA clones for the actin-encoding gene were isolated and characterized from Pneumocystis carinii purified from immunosuppressed rat lungs. The nucleotide sequence encodes a protein of 376 amino acids. The predicted actin protein of P. carinii shares a high degree of conservation to other known actins. Only one major actin gene was found in P. carinii. The P. carinii actin sequence was compared with 30 other actin sequences. Gene phylogenies constructed using both neighbor-joining and protein parsimony methods places the P. carinii actin sequence closest to the majority of the fungi. Since the phylogenetic relationship of P. carinii to fungi and protists has been questioned, these data on the actin gene phylogeny support the grouping of P. carinii with the fungi.     

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.      

Clostridium thermocellum: Adhesion and sporulation while adhered to cellulose and hemicellulose

Summary During growth in the presence of fibers composed of cellulose or hemicellulose, various strains of the thermophilic soil bacterium Clostridium thermocellum and several newly isolated thermophilic anaerobic soil bacteria adhered to the fibers. Attachment occurred via a fibrous ruthenium red-staining material. C. thermocellum sporulated while attached to the fibers when the pH dropped below 6.4. It is postulated that the attachment is involved in cellulose breakdown and that C. thermocellum gaines an advantage by remaining attached to its insoluble substrates when the environment is not suitable for rapid growth. The tendency to adhere to cellulose fibers was used in the purification of thermophilic cellulolytic anaerobes.     

Wall and membrane biogenesis in the unusual labyrinthulid-like organismSorodiplophrys stercorea

Summary Electron microscopic investigations show the scale subunits of the walls ofSorodiplophrys stercorea to be produced by the Golgi apparatus. Their chief monosaccharide subunit is identified tentatively as arabinose. Membrane flow involving the nuclear envelope, endoplasmic reticulum, Golgi apparatus, Golgi vesicles, plasmalemma, and possibly prominent refractive bodies composed of membranes is suggested. Cytochemical data supporting ultrastructural evidence concerning the sites of scale and membrane biogenesis are presented.     

The role of snail aestivation in transmission of schistosomiasis in changing climatic conditions

Schistosomiasis vector snails are subjected to extreme seasonal changes, particularly in ephemeral rivers and lentic waterbodies. In the tropics, aestivation is one of the adaptive strategies for survival and is used by snails in times of extremely high temperatures and desiccation. Aestivation therefore plays an important role in maintaining the transmission of schistosomiasis. This review assesses the possible impacts of climate change on the temporal and spatial distribution of schistosomiasis-transmitting snails with special emphasis on aestivation, and discusses the effect of schistosome infection on aestivation ability. The impacts of parasite development on snails, as well as physiological changes, are discussed with reference to schistosomiasis transmission. This review shows that schistosome-infected snails have lower survival rates during aestivation, and that those that survive manage to get rid of the infection. In general, snail aestivation ability is poor and survival chances diminish with time. Longer dry periods result in fewer, as well as uninfected, snails. However, the ability of the surviving snails to repopulate the habitats is high.     

Attenuation of pattern recognition receptor signaling is mediated by a MAP kinase kinase kinase

Pattern recognition receptors (PRRs) play a key role in plant and animal innate immunity. PRR binding of their cognate ligand triggers a signaling network and activates an immune response. Activation of PRR signaling must be controlled prior to ligand binding to prevent spurious signaling and immune activation. Flagellin perception in Arabidopsis through FLAGELLIN‐SENSITIVE 2 (FLS2) induces the activation of mitogen‐activated protein kinases (MAPKs) and immunity. However, the precise molecular mechanism that connects activated FLS2 to downstream MAPK cascades remains unknown. Here, we report the identification of a differentially phosphorylated MAP kinase kinase kinase that also interacts with FLS2. Using targeted proteomics and functional analysis, we show that MKKK7 negatively regulates flagellin‐triggered signaling and basal immunity and this requires phosphorylation of MKKK7 on specific serine residues. MKKK7 attenuates MPK6 activity and defense gene expression. Moreover, MKKK7 suppresses the reactive oxygen species burst downstream of FLS2, suggesting that MKKK7‐mediated attenuation of FLS2 signaling occurs through direct modulation of the FLS2 complex.     

Differential indicators of loneliness among elderly. The importance of type of partner relationship, partner history, health, socioeconomic status and social relations

Using data from the 1992 NESTOR-survey 'Living arrangements and social networks of older adults' (N = 4494), the aim of the present study is to identify specific categories of older adults who are most vulnerable to loneliness. By looking at different types of partner relationships (first, second, and third marriages; consensual unions; partners who are not household members) and at partner histories (never married, ever divorced, ever widowed, remarried), this study elaborates on previous research which has tended to look only at the presence versus the absence of partner relationships. Findings indicate that different types of partner relationships provide differential protection against loneliness. There appears to be a 'shadow of the past' of a previous divorce or widowhood in second and third partnerships, which accounts for generally higher levels of loneliness. Single men tend to be more lonely than single women. Moreover, there are no differences in loneliness between men who have always been single and those previously married. Among single women, differences in partner history are relevant: never married single women tend to be least vulnerable to loneliness. The differences in loneliness between older adults with different types of partner relationships and partner histories are only partially attributable to network and social participation differences. The latter independently contribute to the explanation of loneliness. The role of non-social determinants (health and socioeconomic position) is also examined. The results underscore the socially isolating effects of sensory impairments. Older adults with functional limitations, and those with visual or auditory problems tend to be more lonely, findings which are only partially attributable to differences in the number and quality of social relationships. Socioeconomic circumstances primarily have an indirect influence on loneliness. Those with higher levels of educational attainment and higher incomes tend to have more extensive social networks and are therefore less prone to loneliness.     

Floating the raft hypothesis for immune receptors: access to rafts controls receptor signaling and trafficking

The B cell antigen receptor (BCR) is a member of an important family of multichain immune recognition receptors, which are complexes composed of ligand-binding domains associated with signal-transduction complexes. The signaling components of these receptors have no inherent kinase activity but become tyrosine phosphorylated in their cytoplasmic domains by Src-family kinases upon oligomerization, thus initiating signaling cascades. The BCR is unique in this family in that, in addition to its signaling function, it also serves to deliver antigen to intracellular compartments where the antigen is processed and presented bound to major histocompatibility complex (MHC) class II molecules. Recent evidence indicates that both the signaling and antigen-trafficking functions of the BCR are regulated by cholesterol- and sphingolipid-rich plasma membrane microdomains termed rafts. Indeed, upon oligomerization, the BCR translocates into rafts that concentrate the Src-family kinase Lyn and is subsequently internalized directly from the rafts. Thus, translocation into rafts allows the association of the oligomerized BCR with Lyn and the initiation of both signaling and trafficking. Significantly, the access of the BCR to rafts appears to be controlled by a variety of B lymphocyte co-receptors, as well as factors including the developmental state of the B cell and viral infection. Thus, the translocation of the immune receptors into signaling-competent microdomains may represent a novel mechanism to initiate and regulate immune-cell activation.