Inheritance of weight in Rhipicephalus appendiculatus ticks (Acari: Ixodidae) in the laboratory

A selection of the 10% lightest and 10% heaviest males and females of a population of individually weighed Rhipicephalus appendiculatus Neumann adults was made in two experiments. The offspring of homologous pairs were followed until the next adult stage (light x light, control x control and heavy x heavy). The engorged nymphal weights, unfed adult weights, engorged female weights of the parents, egg mass weights, egg weights, larval scutal lengths, engorged larval weights, unfed nymphal weights, engorged nymphal weights and adult weights of the progeny were determined. No significant differences could be demonstrated between the two lines for egg weight, larval scutal length, engorged larval weight and unfed nymphal weight. Significant differences were found between the egg masses, engorged nymphal weights and adult weights of the two lines. The heritability coefficients of body weight determined from adult to adult were 0.14 and 0.10, respectively, during the first and second experiments. Considering females and males separately, the coefficients were 0.10 and 0.18 during the frist experiment and 0.12 and 0.09 during the repeat experiment respectively.     

Kin cohesiveness and possible inbreeding in the mouthbrooding tilapia Sarotherodon melanotheron (Pisces Cichlidae)

Four microsatellite markers were used to study genetic variation among individuals of the mouthbrooding tilapia Sarotherodon melanotheron (Rüppel 1852) caught in separate but adjacent shoals. A comparison was also made with fish from six other localities. Populations originating from riverine environments appear to be panmictic, while samples from open waters such as lagoons showed highly significant heterozygote deficiencies. For instance, at the 33-allele locus SMEL4, 32 homozygous individuals were observed among the 82 individuals from the same lagoon location instead of only five homozygotes expected if random mating occurred. A further assessment of the genetic similarity of individuals within each shoal, validated by robust permutation techniques requiring no precise knowledge of gene frequencies, showed that related individuals tend to aggregate, and suggested that mating occurs preferentially within small groups of kin. Cichlids are often presented as a group of fish where microallopatric speciation takes place. The possible link between kin aggregation, inbreeding and shoaling behaviour we propose here may have important consequences for our understanding of the mechanisms involved in this fast speciation process.     

Solution conformations of early intermediates in Mos1 transposition

DNA transposases facilitate genome rearrangements by moving DNA transposons around and between genomes by a cut-and-paste mechanism. DNA transposition proceeds in an ordered series of nucleoprotein complexes that coordinate pairing and cleavage of the transposon ends and integration of the cleaved ends at a new genomic site. Transposition is initiated by transposase recognition of the inverted repeat sequences marking each transposon end. Using a combination of solution scattering and biochemical techniques, we have determined the solution conformations and stoichiometries of DNA-free Mos1 transposase and of the transposase bound to a single transposon end. We show that Mos1 transposase is an elongated homodimer in the absence of DNA and that the N-terminal 55 residues, containing the first helix-turn-helix motif, are required for dimerization. This arrangement is remarkably different from the compact, crossed architecture of the dimer in the Mos1 paired-end complex (PEC). The transposase remains elongated when bound to a single-transposon end in a pre-cleavage complex, and the DNA is bound predominantly to one transposase monomer. We propose that a conformational change in the single-end complex, involving rotation of one half of the transposase along with binding of a second transposon end, could facilitate PEC assembly.     

Geographic differentiation of the mitochondrial genome in Mus spretus Lataste

Analysis of mitochondrial DNA variability of the Mouse M. spretus over its whole living area reveals genetic isolation and phylogenetic independence of two geographical groups. The recent history of the species is discussed in the light of these data.     

Nonsense Mutations in the Maltose A Region of the Genetic Map of Escherichia coli

The isolation of one amber mutation in malQ, one ochre mutation in malP, and seven amber mutations in malT is reported. A study of their phenotypic expressions in the presence of the amber suppressor su(III) and the ochre suppressor su(c) suggests that (i) malQ is the structural gene for amylomaltase; (ii) malQ and the structural gene for maltodextrin phosphorylase, malP, belong to the same operon; (iii) the malT product, which promotes the expression of the malP-malQ operon, is a protein synthesized in limiting amounts by the wild-type strain.     

The inherent flexibility of type I non-ribosomal peptide synthetase multienzymes drives their catalytic activities

Non-ribosomal peptide synthetases (NRPSs) are multienzymes that produce complex natural metabolites with many applications in medicine and agriculture. They are composed of numerous catalytic domains that elongate and chemically modify amino acid substrates or derivatives and of non-catalytic carrier protein domains that can tether and shuttle the growing products to the different catalytic domains. The intrinsic flexibility of NRPSs permits conformational rearrangements that are required to allow interactions between catalytic and carrier protein domains. Their large size coupled to this flexibility renders these multi-domain proteins very challenging for structural characterization. Here, we summarize recent studies that offer structural views of multi-domain NRPSs in various catalytically relevant conformations, thus providing an increased comprehension of their catalytic cycle. A better structural understanding of these multienzymes provides novel perspectives for their re-engineering to synthesize new bioactive metabolites.