Molecular Evolution of Cytochrome b of Subterranean Mole Rats, Spalax ehrenbergi Superspecies, in Israel

We describe the molecular evolution of cytochrome b of blind subterranean mole rats. We examined 12 individuals for nucleotide differences in the region of 402 base pairs of mitochondrial cytochrome b. Each individual represents a different population from the entire ecological and speciational range of the four chromosomal species in Israel (2n= 52, 54, 58, and 60) belonging to the Spalax ehrenbergi superspecies. Our results indicate the following. (i) There are seven first-position transitional differences, compared to 34 variable third positions, with no observed second-position substitutions. (ii) A maximum of four amino acids differences occurs across the range. (iii) Within-species diversity increases southward. Only 1 autoapomorphic substitution characterizes either 2n= 52 or 2n= 54, but 6–11 substitutions characterize 2n= 58, and 9–13 substitutions characterize 2n= 60. (iv) Both parsimony and maximum-likelihood trees suggest two monophyletic groups: (a) 2n= 52 and 54, and (b) 2n= 58 and 60, as identified earlier by other protein and DNA markers. (v) Mitochondrial cytochrome b heterogeneity is significantly correlated with climatic factors (rainfall) and biotic factors (body size and allozymes). We hypothesize that two selective regimes direct cytochrome b evolution in the S. ehrenbergi superspecies: (i) purifying selection in the flooded, mesic, hypoxic northern range of 2n= 52 and 54 and (ii) diversifying selection in the climatically spatiotemporal, xeric, and variable southern range of 2n= 58 and 60. Thus, the molecular evolution of mitochondrial cytochrome b in S. ehrenbergi is explicable by opposite selective stresses across the range of S. ehrenbergi in Israel, associated with the ecological adaptive radiation of the complex. Received: 23 October 1998 / Accepted: 2 May 1999     

Nucleotide sequence of the Escherichia coli hisD gene and of the Escherichia coli and Salmonella typhimurium hisIE region

Summary In this paper we report the nucleotide sequence of the hisD gene of Escherichia coli and of the hisIE region of both E. coli and Salmonella typhimurium. The hisD gene codes for a bifunctional enzyme, l-histidinol: NAD⁺ oxidoreductase, of 434 amino acids with a molecular mass of 46,199 daltons. We established that the hisIE region of both S. typhimurium and E. coli is composed of a single gene and not, as previously believed, of two separate genes. The derived amino acid sequence indicates that the hisIE gene codes for a bifunctional protein of 203 amino acids with an approximate molecular mass of 22,700 daltons. We also determined the nucleotide sequence of a deletion mutant in S. typhimurium which abolishes the hisF and hisI functions but retains the hisE function. We deduced that the mutant produces a chimeric protein fusing the aminoterminal region of the upstream hisF gene to the carboxylterminal domain of the hisIE gene which encodes for the hisE function. In view of these results the structural and functional organization of the histidine operon in enteric bacteria needs to be revised. The operon is composed of only 8 genes and the pathway leading to the biosynthesis of the amino acid requires 11 enzymatic steps.     

Security Implications of Typical Grid Computing Usage Scenarios

Grid Computing consists of a collection of heterogeneous computers and resources spread across multiple administrative domains with the intent of providing users uniform access to these resources. There are many ways to access the resources of a Grid, each with unique security requirements and implications for both the resource user and the resource provider. A comprehensive set of Grid usage scenarios is presented and analyzed with regard to security requirements such as authentication, authorization, integrity, and confidentiality. The main value of these scenarios and the associated security discussions is to provide a library of situations against which an application designer can match, thereby facilitating security-aware application use and development from the initial stages of the application design and invocation. A broader goal of these scenarios is to increase the awareness of security issues in Grid Computing.     

Activity-dependent plastic changes in the motor nerve terminals of the adult rat

Summary— Small and short-lasting physiologic variations in the locomotor activity of normal adult rats can induce remodelling in the motor nerve endings of the fast extensor digitorum longus muscle. The specificity and relative importance of the different plastic adaptations occurring in the presynaptic axonal tree have been studied, in silver impregnated nerve endings, by using an automatic image analysis treatment of the nerve terminals' geometric properties and a discriminant analysis of the morphometric parameters. Changes observed, like selective length variations in certain terminal segments and positional rearrangements, agree with a mechanism of neural connectivity regulation in the adult that arises as a consequence of normal neuromuscular activity.     

Phenomenological theory of GC/AT pressure on DNA base composition

Summary We present a phenomenological theory expressing the constraints operating on the (G+C) contents of the three codon positions, i.e., first, second, and third bases of codons, by using the smallest number of constraint parameters having clear physical and genetic meaning. Theoretical curves displaying base composition at each of the three codon sites are given. The agreement between the theoretical curves and the data points of 1277 genes is quite good irrespective of the species from which the DNAs originated; the curves might be universal ones and the constraint parameters might have general biological meanings in relation to the DNA/RNA and protein functions.