Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state

The genes for cellobiose utilization are normally cryptic in Escherichia coli. The cellobiose system was used as a model to understand the process by which silent genes are maintained in microbial populations. Previously reported was (1) the isolation of a mutant strain that expresses the cellobiose-utilization (Cel) genes and (2) that expression of those genes allows utilization of three beta- glucoside sugars: cellobiose, arbutin, and salicin. The Cel gene cluster has now been cloned from that mutant strain. In the course of locating the Cel genes within the cloned DNA segment, it was discovered that inactivation of the Cel-encoded hydrolase rendered the host strain sensitive to all three beta-glucosides as potent inhibitors. This sensitivity arises from the accumulation of the phosphorylated beta- glucosides. Because even the fully active genes conferred some degree of beta-glucoside sensitivity, the effects of cellobiose on a series of five Cel+ mutants of independent origin were investigated. Although each of those strains utilizes cellobiose as a sole carbon and energy source, cellobiose also acts as a potent inhibitor that reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand, wild-type strains that cannot utilize cellobiose are not inhibited. The observation that the same compound can serve either as a nutrient or as an inhibitor suggests that, under most conditions in which cellobiose will be present together with other resources, there is a strong selective advantage to having the cryptic (Cel0) allele. In those environments in which cellobiose is the sole, or the best, resource, mutants that express the genes (Cel+) will have a strong selective advantage. It is suggested that temporal alternation between these two conditions is a major factor in the maintenance of these genes in E. coli populations. This alternation of environments and fitnesses was predicted by the model for cryptic-gene maintenance that was previously published.      

On alternatives to selection-induced mutation in the Bgl operon of Escherichia coli

Selection-induced mutations are nonrandom mutations that occur as specific and direct responses to environmental challenge. Examples of selection-induced mutations have been reported both in bacteria and in yeast. I previously showed (Hall 1988) that excisions of the mobile genetic element IS150 from within bglF are selection induced and argued that they occurred because they were potentially advantageous under the selective conditions employed. Mittler and Lenski (Mittler and Lenski 1992) have argued that such excisions are not selection induced but that they occur randomly in nondividing cells. Here I provide further evidence that IS150 excisions are induced by selection and that the excisions are immediately, rather than only potentially, advantageous to the cell. I also provide evidence that excisions, which Mittler and Lenski claim occur randomly in saturated broth cultures, actually occur after samples from those cultures are plated onto selective medium.      

High-level expression of the Endo-beta-N-acetylglucosaminidase F2 gene in E.coli: one step purification to homogeneity

The Endo F2gene was overexpressed in E.coli as a fusion protein joined to the maltose-binding protein. MBP-Endo F2was found in a highly enriched state as insoluble, inactive inclusion bodies. Extraction of the inclusion bodies with 20% acetic acid followed by exhaustive dialysis rendered the fusion protein active and soluble. MBP-Endo F2was digested with Factor Xaand purified on Q-Sepharose. The enzyme was homogeneous by SDS-PAGE, and appeared as a single symmetrical peak on HPLC. Analysis of the amino-terminus demonstrated conclusively that recombinant Endo F2was homogeneous and identical to the native enzyme.      

Antisecretory factor modulates GABAergic transmission in the rat hippocampus

Antisecretory Factor (AF) is a protein that has been implicated in the suppression of intestinal hypersecretion and inflammation. Intestinal secretion and inflammation are partly under local and central neural control raising the possibility that AF might exert its action by modulating neural signaling. In the present study we have investigated whether AF can modulate central synaptic transmission. Evoked glutamatergic and GABAergic synaptic transmissions were investigated using extracellular recordings in the CA1 region of hippocampal slices from adult rats. AF (0.5 microg/ml) suppressed GABA(A)-mediated synaptic transmission by about 40% while having no effect on glutamatergic transmission. Per oral administration of cholera toxin as well as feeding of rats with a diet containing hydrothermally processed cereals, known to upregulate endogenous AF plasma activity, mimicked the effect of exogenously administered AF on hippocampal GABAergic transmission. Our results identify AF as a neuromodulator and further raise the possibility that the hippocampus and AF are involved in a gut-brain loop controlling intestinal secretion and inflammation.     

Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae)

Individual plants of several Amelanchier taxa contain many polymorphic nucleotide sites in the internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA). This polymorphism is unusual because it is not recent in origin and thus has resisted homogenization by concerted evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the result of gene flow between two major North American clades resolved by phylogenetic analysis of ITS sequences. Western North American species plus A. humilis and A. sanguinea of eastern North America form one clade (A), and the remaining eastern North American Amelanchier make up clade B. Five eastern North American taxa are polymorphic at many of the nucleotide sites where clades A and B have diverged and are thought to be of hybrid origin, with A. humilis or A. sanguinea as one parent and various members of clade B as the other parent. Morphological evidence suggests that A. humilis is one of the parents of one of the polymorphic taxa, a microspecies that we refer to informally as A. "erecta." Sequences of 21 cloned copies of the ITS1- 5.8S gene-ITS2 region from one A. "erecta" individual are identical to A. humilis sequence or to the clade B consensus sequence, or they are apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier "erecta" and another polymorphic taxon are suspected to be relatively old because both grow several hundred kilometers beyond the range of one of their parents. ITS sequence polymorphisms have apparently persisted in these two taxa perhaps because of polyploidy and/or agamospermy (asexual seed production), which are prevalent in the genus.      

Lysine acetylome profiling uncovers novel histone deacetylase substrate proteins in Arabidopsis

Histone deacetylases have central functions in regulating stress defenses and development in plants. However, the knowledge about the deacetylase functions is largely limited to histones, although these enzymes were found in diverse subcellular compartments. In this study, we determined the proteome‐wide signatures of the RPD3/HDA1 class of histone deacetylases in Arabidopsis. Relative quantification of the changes in the lysine acetylation levels was determined on a proteome‐wide scale after treatment of Arabidopsis leaves with deacetylase inhibitors apicidin and trichostatin A. We identified 91 new acetylated candidate proteins other than histones, which are potential substrates of the RPD3/HDA1‐like histone deacetylases in Arabidopsis, of which at least 30 of these proteins function in nucleic acid binding. Furthermore, our analysis revealed that histone deacetylase 14 (HDA14) is the first organellar‐localized RPD3/HDA1 class protein found to reside in the chloroplasts and that the majority of its protein targets have functions in photosynthesis. Finally, the analysis of HDA14 loss‐of‐function mutants revealed that the activation state of RuBisCO is controlled by lysine acetylation of RuBisCO activase under low‐light conditions.     

Arabidopsis At5g39790 encodes a chloroplast-localized,carbohydrate-binding,coiled-coil domain-containing putative scaffold protein

Background  

Starch accumulation and degradation in chloroplasts is accomplished by a suite of over 30 enzymes. Recent work has emphasized the importance of multi-protein complexes amongst the metabolic enzymes, and the action of associated non-enzymatic regulatory proteins. Arabidopsis At5g39790 encodes a protein of unknown function whose sequence was previously demonstrated to contain a putative carbohydrate-binding domain.     

The essential role of lipids in Alzheimer's disease

In the absence of efficient diagnostic and therapeutic tools, Alzheimer's disease (AD) is a major public health concern due to longer life expectancy in the Western countries. Although the precise cause of AD is still unknown, soluble β-amyloid (Aβ) oligomers are considered the proximate effectors of the synaptic injury and neuronal death occurring in the early stages of AD. Aβ oligomers may directly interact with the synaptic membrane, leading to impairment of synaptic functions and subsequent signalling pathways triggering neurodegeneration. Therefore, membrane structure and lipid status should be considered determinant factors in Aβ-oligomer-induced synaptic and cell injuries, and therefore AD progression. Numerous epidemiological studies have highlighted close relationships between AD incidence and dietary patterns. Among the nutritional factors involved, lipids significantly influence AD pathogenesis. It is likely that maintenance of adequate membrane lipid content could prevent the production of Aβ peptide as well as its deleterious effects upon its interaction with synaptic membrane, thereby protecting neurons from Aβ-induced neurodegeneration. As major constituents of neuronal lipids, n-3 polyunsaturated fatty acids are of particular interest in the prevention of AD valuable diet ingredients whose neuroprotective properties could be essential for designing preventive nutrition-based strategies. In this review, we discuss the functional relevance of neuronal membrane features with respect to susceptibility to Aβ oligomers and AD pathogenesis, as well as the prospective capacities of lipids to prevent or to delay the disease.     

Mate choice copying and conspecific cueing in Japanese quail, Coturnix coturnix japonica

In four experiments, we examined the effects on the affiliative preferences of 'focal' female Japanese quail given the opportunity to watch a conspecific male interact with a 'model' female. Experiments were conducted in three, 10-min phases: (1) a pretest, during which a 'focal' female chose between two males; (2) an observation phase, when each focal female watched the male she had spent less time near during the pretest (her 'nonpreferred' male) interact with a 'model' quail; and (3) a post-test, during which each focal female again chose between her nonpreferred and preferred males. Focal females increased their preferences for nonpreferred males after seeing them together with a model female (but not a model male), even if the nonpreferred male and model female were separated by an opaque barrier that prevented them from interacting. A focal female's preference for the end of the enclosure containing her nonpreferred male was not increased when she either watched him court a concealed model female or watched a model female that was being courted by him. Taken together, the present results suggest that a simple tendency for females to approach areas where they have previously seen a male and female quail, in preference to locations where they have seen only a male quail, can explain some of the effect of watching a nonpreferred male mate on a female's tendency to affiliate with him. However, focal females also showed enhanced preferences for nonpreferred males they had seen mating after we both moved those males and controlled for effects of transposition. Thus, processes akin to both 'mate choice copying' and 'conspecific cueing' remain viable explanations for the increase in a focal female quail's tendency to affiliate with a male she watched mate with another female. Copyright 1999 The Association for the Study of Animal Behaviour.     

Resistance to serum killing may contribute to differences in the abilities of capsulate and non-capsulated isolates of lactococcus garvieae to cause disease in rainbow trout (Oncorhynchus mykiss L.)

Three capsulated and two non-capsulated isolates of Lactococcus garvieae were investigated in terms of their wall proteins, virulence and interactions with rainbow trout immunoglobulin (Ig). All isolates were similar in integral membrane protein profile, and all were able to bind non-immune rainbow trout Ig, although different proteins appeared to be involved in Ig binding. However, whilst capsulated isolates were highly virulent, non-capsulated isolates were avirulent. This appeared to correlate with susceptibility of the non-capsulated isolates to rainbow trout normal serum. In contrast, the capsulated isolates were resistant to both normal and immune serum killing. In spite of this, passive immunisation of rainbow trout with specific anti-serum to L. garvieae was able to protect against challenge by capsulated isolates of L. garvieae. This suggests the antibody may have some other role in protection against disease caused by this important Gram-positive bacterial fish pathogen.