Characterization of the bacteriophage lambda excisionase (Xis) protein: the C-terminus is required for Xis-integrase cooperativity but not for DNA binding.

We have performed a mutational analysis of the xis gene of bacteriophage lambda. The Xis protein is 72 amino acids in length and required for excisive recombination. Twenty-six mutants of Xis were isolated that were impaired or deficient in lambda excision. Mutant proteins that contained amino acid substitutions in the N-terminal 49 amino acids of Xis were defective in excisive recombination and were unable to bind DNA. In contrast, one mutant protein containing a leucine to proline substitution at position 60 and two truncated proteins containing either the N-terminal 53 or 64 amino acids continued to bind lambda DNA, interact cooperatively with FIS and promote excision. However, these three mutants were unable to bind DNA cooperatively with Int. Cooperativity between wild-type Xis and Int required the presence of FIS, but not the Int core-type binding sites. This study shows that Xis has at least two functional domains and also demonstrates the importance of the cooperativity in DNA binding of FIS, Xis and Int in lambda excision.     

The putative mitochondrial genome of Plasmodium falciparum

Intraerythrocytic stages of mammalian malarial parasites employ glycolysis for energy production but some aspects of mitochondrial function appear crucial to their survival since inhibitors of mitochondrial protein synthesis and electron transport have antimalarial effects. Investigations of the putative mitochondrial genome of Plasmodium falciparum have detected organellar rRNAs and tRNAs encoded by a 35 kb circular DNA. Some features of the organization and sequence of the rRNA genes are reminiscent of chloroplast DNAs. The 35 kb DNA also encodes open reading frames for proteins normally found in chloroplast but not mitochondrial genomes. An apparently unrelated 6 kb tandemly repeated element which encodes two mitochondrial protein coding genes and fragments of rRNA genes is also found in malarial parasites. The malarial mitochondrial genome thus appears quite unusual. Further investigations are expected to provide insights into the possible functional relationships between these molecules and perhaps their evolutionary history.     

Have malaria parasites three genomes?

Recent efforts to define the mitochondrial genome of malaria parasites have uncovered an unexpected complexity: there are two almost totally dissimilar organellar DNA molecules. lain Wilson, Malcolm Gardner, Jean Feagin and Donald Williamson discuss the surprising possibility that Plasmodium may have, in addition to the nuclear genome, two unrelated organellar genomes, one evidently mitochondrial and the other of unknown function.     

Mapping of mouse gamma crystallin genes on chromosome 1

Restriction fragments analysis of DNA from mouse-hamster somatic-cell hybrid clones revealed that a mouse gamma crystallin cDNA hybridized to genomic sequences located on mouse chromosome 1. Identification of restriction fragment length polymorphisms (RFLPs) in the gamma crystallin sequences of inbred strains of mice permitted the further localization of the gamma crystallin genes (Cryg) to the proximal region of chromosome 1 closely linked to the loci encoding isocitrate dehydrogenase (Idh-1), a low molecular weight (LM) crystallin protein polymorphism (Len-1), and fibronectin (Fn-1). A single recombinant was observed betweenLen-1 and an RFLP in the gamma crystallin gene family, consistent with the hypothesis thatLen-1 is one of the several structural loci encoding gamma crystallin genes.Len-1 is probably located on the centromeric end of theCryg gene family. Linkage ofIdh-1, Cryg, andFn-1 in mice extends the syntenic relationship of those loci to the human, bovine, and rodent genomes and may define a chromosomal region that is generally conserved among mammals. The map position ofCryg, near the eye lens obsolescence (Elo) locus, was confirmed by the discovery that the restriction fragment patterns of gamma crystallin sequences differed between strain C3H/HeJ and the congenic anophthalmic mutant strain, C3H.Elo. Therefore, the gamma crystallin genes were contransferred with the mutantElo gene in the derivation of C3H.Elo. The results establish that LEN-1 is a marker for the gamma crystallin gene family, position the gamma crystallin gene family relative to other markers on mouse chromosome 1, and provide additional evidence that theElo mutation is encoded at a locus closely linked to the gamma crystallin gene cluster. This study found no evidence of recombination hot spots within the gamma crystallin gene cluster.     

The interaction of pH and cyclic adenosine 3',5'-monophosphate on activation of motility in Triton X-100 extracted bull sperm

The motility of demembranated bull sperm was found to be governed by the concentrations of cyclic adenosine 3', 5'-monophosphate (cAMP) and Ca2+ at low pH (6.6-7.1), and was less sensitive to these variables at higher pH (7.4-7.8). Although motility was generally found to increase with increasing pH in the range from 6.6 to 7.8, the addition of exogenous cAMP markedly and selectively improved the motility at the lower end of the range (pH 6.6-7.1). In the presence of 10 microM cAMP, low Ca2+ (8.0 X 10(-8) M), and a high concentration of Mg-adenosine 5'-triphosphate (ATP, 8 mM), demembranated sperm at pH 6.8 and 7.1 exhibited swimming similar to that of live ejaculated sperm. At a free Ca2+ concentration of 4.4 X 10(-5) M, the motility was rapidly inhibited at pH 6.8-7.1, whereas at pH 7.4-7.8, the activity was not greatly affected. Since calcium is known to antagonize the cAMP pathway by activating Ca2+-dependent phosphodiesterase and Ca2+-dependent phosphatase, this further supports the idea that cAMP-dependent activation is crucial for motility at low pH. Our results demonstrate that the flagellar axoneme can function normally at relatively acidic pH, and produce vigorous swimming at high levels of ATP. The ATP content of live sperm was measured and found to be high enough (approximately 8 mM) to support the vigorous motility seen at pH 6.6-7.1 in the models.(ABSTRACT TRUNCATED AT 250 WORDS)     

Somatosensory cortical mechanisms of feature detection in tactile and kinesthetic discrimination

Neurons in somatosensory cortex of primates process sensory information from the hand by integrating information from large populations of receptors to extract specific features. Tactile neurons in areas 1 and 2 are shown to select features such as contact area, edge orientation, motion across the skin, or direction of movement. Features coded by kinesthetic neurons in areas 3a and 2 relate to joint movement, the joint angle around which the movement occurs, or coordinated postures of the hand and arm. An even higher order cortical cell integrates tactile and kinesthetic information; these "haptic neurons" respond optimally to contact of objects actively grasped in the hand. These global features are coded at the expense of loss of information concerning fine-grained spatial detail.     

Reconstruction of a type-B configuration monkey Sertoli cell: size, shape, and configurational and specialized cell-to-cell relationships

A model of a stage-V monkey Sertoli cell was reconstructed from electron micrographs taken of semiserial sections. The configuration (type-B) was one in which spermatids were positioned near the lumen, their heads occupying shallow cylindrical recesses at the apical portion of the Sertoli cell. The cell volume was calculated to be 4,100 micron3, the surface area 2,400.68 micron2, and the surface-to-volume ratio 0.58:1. The reconstructed cell extended from the basal lamina to the tubular lumen and was generally of the tall columnar type although its surface contour was highly irregular. The dimensions of the cell [centripetal (68.46 micron), circumferential (18.40 micron), and longitudinal (21.63 micron)] were determined and cell surfaces designated. Relative and absolute surface areas of the reconstructed cell which faced other Sertoli cells, germ cells, basal lamina, and tubular lumen were calculated. Junctions and surface specializations were enumerated, catalogued, and depicted on diagrams of the cell surface. Where appropriate, type-A rat and type-B monkey Sertoli cells were compared and discussed. Morphometry was utilized to analyze the relative surface areas of germ cells adjoining the reconstructed cell to determine the percentage of their surface facing cellular and acellular elements, and these data were compared to data obtained for the rat.     

Effects of tunicamycin on the expression and function of formyl peptide chemotactic receptors of differentiated HL-60 cells

We previously showed that formyl peptide chemotactic receptors (FPCR) of human phagocytic cells contain at least two asparagine-linked oligosaccharide chains located at the distal end of the receptor. The requirement of these N-linked oligosaccharide chains for expression and function of FPCR was investigated in HL-60 cells induced to differentiate by N6,O2-dibutyryladenosine 3',5'-monophosphate (Bt2cAMP) in the presence or absence of 5 micrograms/ml tunicamycin. Tunicamycin did not prevent the changes in morphology associated with Bt2cAMP-induced differentiation of HL-60 cells. Autoradiographic analysis after SDS-PAGE of FPCR affinity labeled with N-formyl-Nle-Leu-Phe-Nle-[125I]iodo-Tyr-Lys (formyl 125I-hexapeptide) and ethylene glycol bis(succinimidyl succinate) demonstrated that greater than 95% of FPCR expressed by tunicamycin-treated cells completely lacked N-linked oligosaccharide (Mr 32,000), and no fully glycosylated FPCR (Mr 62,000 to 85,000) was detectable. Scatchard analysis of formyl 125I-hexapeptide binding indicated the presence of two classes of binding sites for both control and tunicamycin-treated cells (control cells, 82,000 +/- 32,000 sites/cell with Kd 10.0 +/- 4.3 nM and 520,000 +/- 40,000 sites/cell with Kd 250 +/- 80 nM; tunicamycin-treated cells, 11,000 +/- 5000 sites/cell with Kd 3.0 +/- 1.9 nM and 470,000 +/- 70,000 sites/cell with Kd of 500 +/- 140 nM). Both control and tunicamycin-treated cells augmented superoxide anion release, exhibited a migratory response, and showed a transient rise in intracellular free Ca2+ upon stimulation with N-formyl-Nle-Leu-Phe. However, the responses of the tunicamycin-treated cells were less than that of the control cells. The present studies demonstrate that N-glycosylation of FPCR is not essential for cell surface expression or for several FPCR-mediated cell responses.     

Characterisation of the arrestment responses of Trichogramma evanescens

Summary Contact kairomones and oviposition in a host egg stimulated arrestment behaviour in Trichogramma evanescens, characterised by a reduction in walking speed and increased turning. Previous oviposition experience did not influence a parasitoid's response to contact kairomones, but successive encounters with kairomone patches resulted in parasitoids habituating to the contact chemical. Oviposition on a kairomone patch did not reverse this habituation effect. It was concluded that contact kairomones and host eggs will both contribute independently to the duration of a patch visit. The selection of patches by T. evanescens will depend on its response to kairomones. Results from this study indicate that the application of contact kairomones to field crops will not necessarily increase the probability of parasitoids finding hosts.