Transductional analysis of chromosome replication time

Summary Following transduction of exponentially growing cultures of Escherichia coli with phage P1, cells with recombinant phenotype begin to increase in number after an initial lag of about one generation time. We show that transductants for markers located at different positions on the chromosome begin to increse at different times, in reverse order to that in which they are replicated. The period over which this happens is equal in duration to the time taken to replicate the chromosome and we have used this relationship to calculate the C-period of E. coli K12 growing at 30°C. We exclude transduction-induced filamentation as the cause of the initial lag and suggest that the lag may result from the way in which donor DNA is inherited.     

The relation between growth, conidiation and trehalase activity in Neurospora crassa

The extent to which trehalose is accumulated in the vegetative mycelium of strains of Neurospora crassa is significantly affected by conidiation. In heavily conidiating strains a rapid decrease in mycelial trehalose occurs following the initiation of conidiation. Meanwhile, trehalase activity in the vegetative mycelium of heavily conidiating strains increases rapidly following the initiation of conidiation, although apparently it is not directly caused by the sporulation process. High levels of both trehalase and trehalose appear concomitantly in the newly formed conidia.     

Sequential uterine horn versus simultaneous total uterine flush to recover bovine embryos nonsurgically

Beef cows were superovulated with follicle stimulating hormone (FSH) to compare two nonsurgical methods of embryo recovery from the uterus. In the first method each uterine horn was independently flushed with physiological saline solution (PSS) through a Foley catheter passed through the cervix and into the uterine horn. In the second method both uterine horns were simultaneously flushed with PSS by passing the catheter into the uterine body. In both methods, the numbers of ovulations were determined after embryo collection by counting the corpora lutea (CL) on both ovaries of each cow through a flank incision. Independent flushing (n = 19) averaged 6.4 embryos and 16.1 CL per cow for a recovery rate of 40%. Simultaneous flushings (n = 22) averaged 5.4 embryos and 17.7 CL per cow for a recovery rate of 31%. This difference between the recovery rates of the two flushing methods was not significant (P>0.05).     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Tyrosine phosphorylation of focal adhesion kinase at sites in the catalytic domain regulates kinase activity: a role for Src family kinases.

Focal adhesion kinase (FAK) is a widely expressed nonreceptor protein-tyrosine kinase implicated in integrin-mediated signal transduction pathways and in the process of oncogenic transformation by v-Src. Elevation of FAK's phosphotyrosine content, following both cell adhesion to extracellular matrix substrata and cell transformation by Rous sarcoma virus, correlates directly with an increased kinase activity. To help elucidate the role of FAK phosphorylation in signal transduction events, we used a tryptic phosphopeptide mapping approach to identify tyrosine sites of phosphorylation responsive to both cell adhesion and Src transformation. We have identified four tyrosines, 397, 407, 576, and 577, which are phosphorylated in mouse BALB/3T3 fibroblasts in an adhesion-dependent manner. Tyrosine 397 has been previously recognized as the major site of FAK autophosphorylation. Phosphorylation of tyrosines 407, 576, and 577, which are previously unrecognized sites, is significantly elevated in the presence of c-Src in vitro and v-Src in vivo. Tyrosines 576 and 577 lie within catalytic subdomain VIII--a region recognized as a target for phosphorylation-mediated regulation of protein kinase activity. We found that maximal kinase activity of FAK immune complexes requires phosphorylation of both tyrosines 576 and 577. Our results indicate that phosphorylation of FAK by Src (or other Src family kinases) is an important step in the formation of an active signaling complex.     

Age determination and body growth of the Common duiker Sylvicapra grimmia(Mammalia)

Age determination in the Common duiker Sylvicapra grimmia was investigated by analysis of tooth eruption and replacement sequence, incremental lines of tooth cementum and tooth wear in a unique collection of 48 known-age skulls, and also by analysis by post-natal body growth in known-age duiker. In both the mandible and maxilla, permanent molariform teeth were fully erupted and in wear by 26 months of age. There was little variation in the age of eruption and replacement of all molariform teeth, making this a particularly useful feature of the duiker for age determination purposes. In contrast, the variability in eruption of the incisiforms, coupled with the difficulty in distinguishing deciduous incisiforms from the permanent counterparts, placed an unexpected limitation on the use of these teeth. Although the apparent linear relationship between tooth attrition and age has potential for further investigation as an age determination technique, the cementum annuli were not correlated with chronological age. Theoretical Von Bertalanffy equations were used to analyse body growth with age. It was concluded that because the asymptote of growth was reached at such an early age, and because there is so much individual variation in growth, body growth, including horn growth, is of very limited value for age determination. Female duiker were significantly larger than males.     

Chromatin structure during the prereplicative phases in the life cycle of mammalian cells

The object of this study was to determine the kinetics of chromosome decondensation during the G₁ period of the HeLa cell cycle. HeLa cells synchronized in the G₁ period following the reversal of mitotic block were fused with Colcemid-arrested mitotic HeLa cells at 1.5, 3, 5, and 7 h after the reversal of N₂O block. The resulting prematurely condensed chromosomes (PCC) were classified into six categories depending on the degree of their condensation. The frequency of occurrence of each category was plotted as a function of time after mitosis. The results of this study indicate that the process of chromosome decondensation, initiated during the telophase of mitosis continues throughout the G₁ period without any interruption, thus the chromatin reaches an ultimate state of decondensation by the end of G₁ period, when DNA synthesis is initiated.