Paddle cilia and discocilia — Genuine structures?

Kinocilia of epidermal sensory cells in fixed marine Turbellaria often terminate as flattened biconcave discs. The distal part of the ciliary axoneme curves back upon itself forming a 360 degree loop which is enveloped by the plasmalemma. In living animals this structure can be induced by the addition of sodium cacodylate, monobasic sodium phosphate, dibasic sodium phosphate, sucrose, calcium chloride, or formaldehyde to the sea water. Specimens treated with sodium chloride, glutaraldehyde, or osmium tetroxide do not show modified cilia. In animals prepared for EM at low temperature and with a buffered hypotonic fixative less kinocilia are modified than in animals treated with a buffered iso- or hypertonic fixative and at a higher temperature. It is assumed that the unusually shaped cilia, described as "paddle cilia" or "discocilia" in other invertebrates, do not represent a genuine but an artificial structure.     

Monociliary receptors in interstitial Proseriata and Neorhabdocoela (Turbellaria Neoophora)

Summary The ultrastructure of monociliary receptors in 10 species of the Proseriata and Neorhabdocoela is described, with particular reference to the epidermal dendritic part.Sensory cells with a single kinocilium situated at the level of the distal epidermis membrane are considered as mechano- or chemoreceptors.There exist sensory cells with a dendrite penetrating one epidermis cell and bearing an embedded kinocilium and a collar of 8 stereocilia or ridges with a fribrillose substructure. These collared receptors probably function as mechanoreceptors.In comparison with collared sensory cells in species of other turbellarian orders, the embedded receptors in the Proseriata and Neorhabdocoela are more advanced and possess synapomorphous characteristics. With the embedded receptors a new evidence is given for the close phylogenetic relationship between the Proseriata and Neorhabdocoela.The distribution of collared cells in the animal system and their phylogenetic implication for a choanoflagellate origin of the Metazoa are briefly discussed.List of abbreviations ar annular rootlet - bm basement membrane - cb crystalline body - cc collar cell - cw cell web - cwt cell web-thickening - d dendrite - kc kinocilium - lm longitudinal musculature - mv microvilli - n nerve - nt neurotubuli - pb parenchymal branches - r rootlet - rd ridges - rh rhabdite - rm ring musculature - sc stereocilia - sd septate desmosomes - tm transversal musculature - u ultrarhabdites - za zonula adhaerens     

Single amino acid substitutions in the B870 alpha and beta light-harvesting polypeptides of Rhodobacter capsulatus. Structural and spectral effects.

To obtain information on the structural and functional role of highly conserved amino acid residues in the B870 alpha and beta light-harvesting polypeptides of Rhodobacter capsulatus, site-directed mutagenesis was performed. 18 mutants with single amino acid substitutions at nine different positions in the B870 antenna polypeptides were prepared in a B800-850-lacking strain. The characterization of the resulting phenotypes was based on a quantification of the core-complex elements (reaction center, light-harvesting polypeptides, bacteriochlorophyll a and carotenoid) and the core-complex spectral characteristics (absorption maximum, absorption coefficient and fluorescence intensity). These data generally showed that strong structural effects were caused by the amino acid substitutions. Thus, the three tryptophan exchanges at the position alpha 8 resulted in either the absence of a core complex (alpha Trp8----Leu), the absence of the core antenna (alpha Trp8----Ala) or a reduction in the carotenoid content (alpha Trp8----Tyr). Likewise, the mutants alpha Pro13Gly (i.e. alpha Pro13----Gly), beta Gly10Val and alpha Phe23Ala demonstrated an abnormal protein/pigment ratio in the core antenna, while a drastically reduced antenna size resulted from the amino acid exchange beta Arg45Asp. In contrast to the structural effects, the absorption maxima and the fluorescence intensities of the mutant antennae differed only slightly from the wild type. The strongest blue shift of the bacteriochlorophyll a (8-11 nm) was induced by substitutions of the Trp at position alpha 43 (alpha Trp43----Ala, Leu or Tyr). Contrary to the other spectral effects, the absorption coefficient of bacteriochlorophyll a was strongly influenced by the amino acid substitutions and varied by 1.6-times less (beta Arg45Asp) and 1.3-times greater (alpha Phe25Ala) than normal. The antenna-free mutant, alpha Trp8Ala, yielded a high rate of B800-850 revertants during phototrophic growth, indicating a direct energy transfer from the B800-850 antenna to the reaction center in these strains. Although conditions for growth were generally observed to influence phenotypic expression, the structural as well as spectral effects were demonstrated to differ to the greatest extent between chemotrophically grown and phototrophically grown cells.     

Primary structure of the herpesvirus saimiri genome.

This report describes the complete nucleotide sequence of the genome of herpesvirus saimiri, the prototype of gammaherpesvirus subgroup 2 (rhadinoviruses). The unique low-G + C-content DNA region has 112,930 bp with an average base composition of 34.5% G + C and is flanked by about 35 noncoding high-G + C-content DNA repeats of 1,444 bp (70.8% G + C) in tandem orientation. We identified 76 major open reading frames and a set of seven U-RNA genes for a total of 83 potential genes. The genes are closely arranged, with only a few regions of sizable noncoding sequences. For 60 of the predicted proteins, homologous sequences are found in other herpesviruses. Genes conserved between herpesvirus saimiri and Epstein-Barr virus (gammaherpesvirus subgroup 1) show that their genomes are generally collinear, although conserved gene blocks are separated by unique genes that appear to determine the particular phenotype of these viruses. Several deduced protein sequences of herpesvirus saimiri without counterparts in most of the other sequenced herpesviruses exhibited significant homology with cellular proteins of known function. These include thymidylate synthase, dihydrofolate reductase, complement control proteins, the cell surface antigen CD59, cyclins, and G protein-coupled receptors. Searching for functional protein motifs revealed that the virus may encode a cytosine-specific methylase and a tyrosine-specific protein kinase. Several herpesvirus saimiri genes are potential candidates to cooperate with the gene for saimiri transformation-associated protein of subgroup A (STP-A) in T-lymphocyte growth stimulation.     

Effects of promoters on the enhancement of pectin methyl esterase expression inAspergillus niger

Summary A pectin methylesterase-encoding gene (pmeA)_has been cloned and transformed intoA. niger wild-type NRRL3. Transformants produced 20-fold more PME than the host strain. For studying the effects of different promoters on thepmeA expression two novel plasmids were constructed, in which thepmeA promoter was replaced by efficient promoters such as theA. nidulans glyceraldehyde-3-phosphate dehydrogenase (pK45) or theA. oryzae -amylase (pK61) promoter. The highest level of PME expression was achieved with theA. oryzae -amylase promoter, reaching a 200-fold increase compared to the production by the host strain.     

3-Phenylpropanoic Acid Improves the Affinity of Ruminococcus albus for Cellulose in Continuous Culture

A continuous-culture device, adapted for use with solid substrates, was used to evaluate the effects of 3-phenylpropanoic acid (PPA) upon the ability of the South African strain Ruminococcus albus Ce63 to ferment cellulose. Steady states of fermentation were established with a dilution rate of 0.17 h⁻¹, and the extent and volumetric rates of cellulose fermentation were determined over four consecutive days. When the growth medium contained no additions (control), 25 μM phenylacetate alone, 25 μM PPA alone, or 25 μM each of phenylacetate and PPA, the extent of cellulose hydrolysis was determined to be 41.1, 35.7, 90.2, and 86.9%, respectively, and the volumetric rate of cellulose hydrolysis was 103.0, 97.9, 215.5, and 230.4 mg liter⁻¹ h⁻¹, respectively. To evaluate the effect of PPA availability on affinity for cellulose, the values for dilution rate and extent of cellulose hydrolysis were used in combination with values for maximum specific growth rate determined from previous studies of growth rates and kinetics of cellulose hydrolysis. The findings support the contention that PPA maintains a competitive advantage for R. albus when grown in a dynamic, fiber-rich environment.     

A morphologic and immunofluorescent analysis of primary guinea pig glomerular cell types grown in chemically defined media. Evidence for clonal growth and cell differentiation

Primary kidney guinea pig glomerular cells were successfully grown in chemically defined media containing insulin, transferrin, and fibronectin or glycylhistidyllysine and fibronectin. Morphologic analysis of glomerular cells grown in either of these chemically defined media provided identical results with respect to cell growth properties and cell types involved. Electron microscopic studies of glomeruli early after they had been placed in culture showed definite evidence of "dedifferentiation" of some glomerular cells. Most glomerular cells in later cultures were undifferentiated. However, since electron microscopic analyses of glomeruli in confluent cultures demonstrated that the majority of cells in culture grow from the epithelial side of the glomerular basement membrane, we suggest that these cells were some form of epithelial cell. This conclusion was further strengthened by the fact that cells resembling well differentiated glomerular epithelial cells were seen in cultures of glomeruli grown in chemically defined media; these cells have never been observed in glomeruli grown in calf serum. Fluorescent microscopy of cell stained with the mitochondrial stain rhodamine 123 allowed identification of several glomerular cell types according to distribution, number, and morphology of mitochondria. Similarly, indirect immunofluorescent microscopy studies using antibodies to fibronectin or laminin provided evidence that glomerular cells separated into cell types according to mitochondrial staining properties were unique biochemically. Using these histochemical criteria it was possible to demonstrate that certain of the glomerular cell types could be selectively grown by addition of the enzyme galactose oxidase to the media. Analysis of our morphologic and histochemical results suggests the possibility that clonal growth and differentiation of glomerular epithelial cells occurs when glomeruli are placed in chemically defined media, and our results are compatible with the hypothesis that either "stem cells" or "dedifferentiated" cells are the primary cells dividing in culture.     

Treadmilling of actin at physiological salt concentrations: An analysis of the critical concentrations of actin filaments

Treadmilling of actin was investigated at physiological salt concentrations (100 mm-KCl, 0.5 to 2.0 mm-MgCl₂, 200 μm-ethyleneglycol-bis(β-aminoethyl ether)N,N′-tetraacetic acid or 50 μm-CaCl₂ at 37 °C. The concentration at which monomers bind to the lengthening end of filaments with the same rate as subunits are released (low critical concentration c₁ was determined by mixing unmodified actin filaments with various concentrations of monomeric actin labeled with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole. Above a monomeric actin concentration of about 0.12 μm, incorporation of actin molecules into filaments was detected, whereas below this concentration no incorporation was found (c₁ = 0.12 μm). Combination of various concentrations of labeled monomers with labeled filaments permitted determination of the net critical concentration ($\text{c}{}_1$) at which filaments lengthen at one end with the same rate as they shorten at the other end ($\text{c}{}_1\text{= 0.16}\text{μm}$). A lower limit of the high critical concentration at the shortening end (c_h) was estimated by measuring the release of subunits from labeled filaments in the presence of various concentrations of unlabeled monomers (c_h >0.5 μm). The differences in the three critical concentrations demonstrate that under physiological conditions actin filaments lengthen at one end by, on the average, one subunit during the time that four association reactions take place at the two ends (efficiency parameters $\text{s =}\text{1}\text{4}$). The small difference between the low and the net critical concentration suggests that the rates of both association and dissociation are considerably greater at the lengthening end than at the shortening end of actin filaments.