Arginine utilization by Mycoplasma fermentans is not regulated by glucose metabolism: A 13C-NMR study

Abstract Electrofusion of protoplasts of two mutant strains of Hansenula polymorpha resulted in high fusion and hybrid yields when the calcium ions present in the conventional fusion medium replaced by zinc ions. The optimal fusion conditions were an alignment field of 0.4 kV cm⁻¹ strength and 2 MHz frequency for 30 s, followed by two consecutive pulses of 12 kV cm⁻¹ strength and 15 μs duration. With 0.05–0.1 mM zinc ions in the fusion medium an average clone number of 10⁴–10⁵ clones per 10⁸ input cells was reached. The presence of about 0.6 mM magnesium ions in the zinc fusion medium was essential.     

Comparison of Southern Appalachian high-elevation outcrop plant communities with their Northern Appalachian counterparts

Abstract. Southern Appalachian high-elevation outcrops harbour six regionally rare Northern Appalachian taxa usually considered relicts of a Pleistocene alpine flora. For five of the six taxa, minimum elevation in the south was 367–1113 m higher than in the north. While habitats compared between the two regions share only 9% of their total flora, individual plots had up to 70% of their species occurring in the opposite region. The northern affinity of southern outcrops increased with elevation, slope steepness, soil Cu, B and SO₄ and decreased with potential solar radiation and soil Na. As a result, communities above 1600 m on felsic bedrock, and above 1350 m on mafic bedrock, were most northern in composition. Northern affinity of southern outcrops also increased with latitude, which may partly result from closer geographic proximity to past communities that provided progenitors for the current northern flora. Northern treeless habitats increased in southern affinity with increased slope steepness, perennial seepage, vegetation height, shade, soil pH, Al, Mn, Na and decreased elevation and organic matter. As a result, northern outcrop communities below treeline were most similar to those on southern outcrops. This suggests that southern outcrop vegetation may be more similar to Pleistocene outcrop vegetation than to Pleistocene alpine vegetation. Partial constrained ordination showed that while compositional differences between the Northern and Southern Appalachian habitats were largely explained by environmental differences, there was a significant component of residual variation explained by north or south position that was unrelated to environment. These residual compositional differences may result from historical influences on community structure involving stochastic extinction and colonization processes.     

Construction of first-generation lactococcal integrative cloning vectors

Using a randomly-cloned, HindIII-digested, chromosomal fragment from Lactococcus lactis subsp. lactis LM0230, first-generation lactococcal integrative cloning vectors were developed. Through dideoxy DNA sequence analysis, the cloned chromosomal DNA fragment was determined to be 1026 base pairs. Southern hybridization studies demonstrated applicability of the integrative vector to other strains of L. lactis and L. lactis subsp. cremoris. Identification of a single NruI site near the middle of the chromosomal fragment allowed insertion of the erythromycin (Em)-resistance (ery ^r) gene obtained from L. lactis IL1837. Integration of the ery ^r gene into the L. lactis LM0230 chromosome was achieved by a Campbell-like recombination. The nisin (Nis)-resistance (nis ^r) gene from L. lactis IL1904 was inserted into the NruI site in a separate clone and integration into the L. lactis LM0230 chromosome was achieved via a replacement recombination event following electroporation of the linearized nis ^r fragment flanked by the cloned chromosomal DNA. Transformants grown in the absence of either Em or Nis for >200 generations and subsequently transferred to various concentrations of the selectable agent confirmed the stability of the integrated genes. Further studies involving the Nis-resistant (Nis ^r ) transformant suggested that the integrated nis ^r gene may be amplifying within the host chromosome. Correspondence to: S. K. Harlander     

Estimates of the Prevalence of Obesity in Canadian Children

Childhood obesity is becoming a topic of great concern due to the rising prevalence of this condition in North America. Studies conducted in the United States have indicated that the prevalence of obesity has increased dramatically over the past few decades. The purpose of this study was to estimate the prevalence of obesity in Canadian children between the ages of 5 and 12 years by examining data from two national and two regional surveys. The 85th percentiles of each of four anthropometric indices derived from large normative populations were used as diagnostic criteria for obesity. As expected, the resulting prevalences varied according to the criteria used. A significant increase in childhood obesity between the 1981 to 1988 national surveys was observed when the three indices which used skinfolds were applied. Weight-for-height percentiles did not indicate an increase in obesity in these samples. Regional samples showed a less than expected prevalence of obesity among the middle-class children and a higher than expected rate among the inner city boys. It can be concluded that there is a need for a defined criteria for identifying obesity in children in order to avoid confusion resulting from the wide variation in estimates of prevalence resulting from different standards and measurements. Using adiposity-based criteria for obesity it was clearly evident that the prevalence of obesity has increased in Canadian children.     

The XcpR protein of Pseudomonas aeruginosa dimerizes via its N-terminus

Extracellular protein secretion by the main terminal branch of the general secretory pathway in Pseudomonas aeruginosa requires a secretion machinery comprising the products of at least 12 genes. One of the components of this machinery, the XcpR protein, belongs to a large family of related proteins distinguished by the presence of a highly conserved nucleotide binding domain (Walker box A). The XcpR protein is essential for the process of extracellular secretion and amino acid substitutions within the Walker A sequence result in inactive XcpR. The same mutations exert a dominant negative effect on protein secretion when expressed in wild-type bacteria. Transdominance of XcpR mutants suggests that this protein is involved in interactions with other components of the secretion machinery or that it functions as a multimer. In this study, the amino-terminal portion of the cI repressor protein of phage λ was used as a reporter of dimerization in Escherichia coli following fusion to full-length as well as a truncated form of XcpR. The cI–XcpR hybrid proteins were able to dimerize, as demonstrated by the immunity of bacteria expressing them to killing by λ phage. The full-length XcpR as well as several deletion mutants of XcpR were able to disrupt the dimerization of the chimeric cI–XcpR protein. The disruption of cI–XcpR dimers using the deletion mutants of XcpR, combined with the analysis of their dominant negative effects on protein secretion, was used to map the minimal dimerization domain of XcpR, which is located within an 85 amino acid region in its N-terminal domain. Taken together, the data presented in this paper suggest that the XcpR protein dimerizes via its N-terminus and that this dimerization is essential for extracellular protein secretion.     

Electrophysiological evidence for the autoregulation of β-cell secretion by insulin

Electrophysiological studies of cultured rat pancreatic β-cells using intracellular microelectrodes show that exogenous insulin over the range of 0.1–10.0 μg/ml inhibits the electrical activity due to 27.8 mM glucose in a dose-related manner. This inhibitory effect is manifested by a mean increase of the membrane potential from about ?20 to ?30 mV and inhibition of the manner of cells impaled showing spike activity from 60 to less than 10%. The inhibitory influence of insulin is rapid occuring within 5 min for the highest level used. The results provide evidence for a negative feedback role of insulin in regulating its own release.     

Parasitoid behaviour: predicting field from laboratory

Abstract.  1. Most of what is known about parasitoid behaviour comes from laboratory observations: field quantitative observations on searching parasitoids are extremely difficult to do and are rare. The basic components of Aphytis melinus 's response to California red scale ( Aonidiella aurantii ) were studied in the laboratory: encounter, rejection, drumming, probing, oviposition, and host-feeding. It was then asked whether these observations provided a reliable guide to behaviour in the field in a situation that was very different from the laboratory.
2. Field observations were carried out on bark on the trunk and interior branches of trees where live scale density is extremely high in patches, dead scale make up 90% of all scale, and could be expected to interfere with Aphytis search.
3. The laboratory observations predicted well the time taken in the field for each basic event (drumming or probing) and average times spent on a scale. Also well predicted were the distributions of times spent on drumming, probing, and total time on a scale. Rejection rates were much higher in the field. Thus, the laboratory studies predicted foraging behaviour in the field with variable success; potential explanations for observed mismatch between laboratory and field and its possible larger implications are discussed.     

Relative affinity of Ca(II) and Mg(II) ions for human and bovine prothrombin and fragment 1

Equilibrium dialysis results are presented for Ca(II) and Mg(II) ion binding to human and bovine prothrombin and fragment 1. Ca(II) ions bind cooperatively, Mg(II) does not.