Divalent cations cooperatively stabilize close membrane contacts in myelin

Intact nerve myelin compacts to a dehydrated structure of closely apposed membranes when exposed to isotonic solutions at least 10 mM in calcium or tetracaine. The repeat period of the membrane pair in the compacted structure measured by X-ray diffraction is about 126 Å in both central and peripheral mammalian nerve myelins whereas the normal periods are about 158 and 178 Å, respectively. The electron density profile of compacted myelin shows an asymmetric membrane unit with thickness similar to that of the symmetric bilayer of flocculated myelin lipids. The centrosymmetrically averaged myelin membrane profile is similar to that of the lipid bilayer except at the surface where residual protein is concentrated. Dispersions of extracted total myelin lipids flocculate under similar conditions to those causing myelin compaction, indicating that similar forces act in both processes. Compaction is always accompanied by lateral segregation of intramembrane particles out of the close-packed domains. Lateral displacement of intramembrane proteins from compacted domains can be driven by the attraction of the lipid surfaces for each other. Rates of compaction vary with compacting reagent, concentration, tissue, and temperature, and probably reflect the permeability of the tissue. Extensive compaction by calcium or tetracaine leads to disruption and vesiculation of the spirally wrapped myelin membranes.     

The ribosomal database project.

The Ribosomal Database Project (RDP) is a curated database that offers ribosome data along with related programs and services. The offerings include phylogenetically ordered alignments of ribosomal RNA (rRNA) sequences, derived phylogenetic trees, rRNA secondary structure diagrams and various software packages for handling, analyzing and displaying alignments and trees. The data are available via ftp and electronic mail. Certain analytic services are also provided by the electronic mail server.     

Reduction in Microtubule Dynamics In Vitro by Brain Microtubule-Associated Proteins and by a Microtubule-Associated Protein-2 Second Repeated Sequence Analogue

Abstract: Microtubule-associated protein (MAP) binding to assembled microtubules (MTs) can be reduced by the addition of polyglutamate without significant MT depolymerization or interference with MT elongation reactions. Ensuing polymer length redistribution in MAP-depleted MTs occurs on a time scale characteristic of that observed with MAP-free MTs. The redistribution phase occurs even in the absence of mechanical shearing and without appreciable effects from end-to-end annealing, as indicated by the time course of incremental changes in polymer length and MT number concentration. We also observed higher rates of MT length redistribution when the [MAP]/[tubulin] ratio was decreased. Together, these results demonstrate that MT length redistribution rates are greatly influenced by MAP content, and the data are compatible with the dynamic instability model. We also found that a peptide analogue corresponding to the second repeated sequence in the MT-binding region of MAP-2 can also markedly retard MT length redistribution kinetics, a finding that accords with the ability of this peptide to promote tubulin polymerization in the absence of MAPs and to displace MAP-2 from MTs. These results provide further evidence that MAPs can modulate MT assembly/disassembly dynamics and that peptide analogues can mimic the action of intact MAPs without the need for three contiguous repeated sequences in the MT-binding region.     

Carbon load in aquatic ecosystems affects the diversity and biomass of water biofilm consortia and the persistence of the pathogen Campylobacter jejuni within them

The influence of carbon load on autochthonous water microflora population distribution and diversity, and on the persistence of Campylobacter jejuni, was examined with a two-stage aquatic biofilm model. Serine was chosen since it is a carbon source utilised by C. jejuni and concentrations were chosen to reflect upper limits of amino acid load reported in surface water. The total viable count of the autochthonous biofilm microflora increased with increasing serine concentration (10-fold and 20-fold with 5 nM and 5 μM serine, respectively), as did the counts of the microflora in the planktonic phase. Differences in biofilm species distribution as determined by culture were small with changes in temperature or the addition of serine; but was markedly affected by serine as determined by light microscopy, becoming more luxuriant and dominated by long filamentous cells. The addition of serine to the water significantly and progressively reduced the persistence of C. jejuni, which decreased by 25% and 50% with serine concentrations of 5 nM and 5 μM respectively. We have demonstrated that carbon load affects the species diversity and density of both the planktonic and biofilm phase of aquatic autochthonous microflora. Although the survival of C. jejuni in water in a culturable form was sufficient for this to be an important vehicle for its transmission, carbon load significantly influenced survival; an increase in serine concentration significantly reduced survival.     

Changes in the Pattern of Twisted Gastrulation Gene Expression Among Drosophila Species

A long-standing hypothesis posits that morphological changes may be more likely to result from changes in regulation of gene expression than from changes in the protein coding sequences of genes. We have compared the expression pattern of the twisted gastrulation (tsg) gene among five Drosophila species: D. melanogaster, D. simulans, D. subobscura, D. mojavensis, and D. virilis. The tsg gene encodes a secreted protein that is required for the specification of dorsal midline fates in the Drosophila early embryo. TSG is unlike other secreted growth and differentiation factors in Drosophila in that its expression pattern can be experimentally varied and still result in normal development. Because of this, its regulatory region may be freer to diverge than that of other developmental genes whose misexpression may lead to lethal defects. Thus, the tsg gene may be a good indicator of the frequency and nature of evolutionary changes affecting patterns of gene expression. Over ∼60 million years (Myr), the tsg gene has retained a dorsal-on/ventral-off pattern and a middorsal region of expression; but there have been marked changes in the middorsal domain of expression as well as the appearance/loss of other domains of expression along the anterior/posterior axis. Changes between closely related species (∼2–5 Myr since divergence) that are not reflected among more distantly related species suggest frequent changes in gene expression over evolutionary time. These changes in gene expression may serve as the raw material for eventual evolutionary changes in morphology. Received: 24 March 1997 / Accepted: 20 June 1997     

Human immunodeficiency virus type 1 Nef associates with a member of the p21-activated kinase family.

Although human immunodeficiency virus (HIV) Nef is essential for the induction of AIDS, its biochemical function has remained an enigma. In this study, HIV Nef protein is shown to associate with a serine-threonine kinase that recognizes histone H4 as a substrate, is serologically related to rat p21-activated kinase (PAK), and is specifically activated by Rac and Cdc42. These characteristics define the Nef-associated kinase as belonging to the PAK family. PAKs initiate kinase cascades in response to environmental stimuli, and their identification as a target of Nef implicates these signaling molecules in HIV pathogenesis and provides a novel target for clinical intervention.     

Strain-induced growth of the immature lung

Zhang, Shaoping, Vicki Garbutt, and John T. McBride.Strain-induced growth of the immature lung. J. Appl. Physiol. 81(4): 1471-1476, 1996.Toinvestigate the relationship between strain and postnatal lung growth,two groups of weanling ferrets were tracheotomized: the study group wasexposed for 2 wk to a continuous positive airway pressure (CPAP) of 6 cmH₂O and the other group wasexposed to atmospheric pressure (control). Total lung capacity after 2 wk was ~40% higher in the CPAP-exposed animals than in the controlanimals (n = 19 for the control groupand 18 for the study group; P < 0.01). CPAP exposure was also associated with increases in lung weightand total lung protein and DNA contents. Lung recoil, measured in asubgroup of animals, was characterized by air-filled and saline-filledstatic expiratory pressure-volume curves. Neither in the air-filledlungs nor in the saline-filled lungs was there a significant differencebetween CPAP-exposed and control animals in lung recoil at equalfractions of total lung capacity. These data indicate that mechanicalstrain was associated with an acceleration of lung growth in immatureferrets. The preservation of volume-corrected lung recoil and theexpected contribution of surface forces and tissue forces to lungrecoil in CPAP-exposed animals suggest that this response did notinvolve simple lung distension but included a remodeling of the lungparenchyma.