The Biology of Gregarina fernandoi n. sp. in the Cockroach Pysnoscelus surinamensis with Observations on its Development and Cytochemical Nature

SYNOPSIS. Gregarina fernandoi n. sp. is a eugregarine. Its structure, development and life history in the gut of the cockroach Pycnoscelus surinamensis are described. It is named as a new species on the basis of its size, nuclear structure, structure and form of the gametocyst and oocyst. Observations were made on the different stages of the parasite and related to the pH of the gut. In the ceca, pH 4.5–5, the parasite was in its early stages of development, in the midgut, pH 6.5–7, it was in syzygy and in the rectum, pH 7.5–8, gametocysts were found.     

Nestmate recognition in sweat bees (Lasioglossum zephyrum): Does an individual recognize its own odour or only odours of its nestmates?

We investigated the olfactory mechanism by which guard bees of Lasioglossum zephyrum decide whether to admit conspecifics to their nests. First we set up colonies of young bees, consisting of sisters from a single family or a mixture of bees from two distinct families. These bees were then introduced into colonies other than their own. Our experimental evidence shows that guards learn the odours of their nestmates, then accept or reject other bees on the basis of the similarity of the latters' odours to those of the guards' nestmates. Guards act as though they do not use their own odour as a reference for nestmate recognition. This recognition mechanism enables individuals with different odours to live together; it may also enhance the operation of kin selection by providing a more complete basis for discriminating relatives from non-relatives. No evidence was found that nestmates acquire one another's odours. Such lack of odour transfer may be characteristic of early stages in the evolution of recognition mechanisms.     

Short repetitive sequences in green algal mitochondrial genomes: potential roles in mitochondrial genome evolution

Current data on green algal mitochondrial genomes suggest an unexpected dichotomy within the group with respect to genome structure, organization, and sequence affiliations. The present study suggests that there is a correlation between this dichotomy on one hand and the differences in the abundance, base composition, and distribution of short repetitive sequences we observed among green algal mitochondrial genomes on the other. It is conceivable that the accumulation of GC- rich short repeated sequences in the Chlamydomonas-like but not Prototheca-like mitochondrial genomes might have triggered evolutionary events responsible for the distinct series of evolutionary changes undergone by the two green algal mitochondrial lineages. The similarity in base composition, nucleotide sequence, abundance, and mode of organization we observed between the short repetitive sequences present in Chlamydomonas-like mitochondrial genomes on one hand and fungal and vertebrate homologs on the other might extend to some of the roles that the short repetitive sequences have been shown to have in the latter. Potential involvements we propose for the short repetitive sequences in the evolution of Chlamydomonas-like mitochondrial genomes include fragmentation and scrambling of the ribosomal-RNA-coding regions, extensive gene rearrangements, coding-region deletions, surrogate origins of replication, and chromosomal linearization.      

Aspergillus terreus and its toxic metabolites as a food contaminant in some Egyptian Bakery products and grains

A. terreus isolates isolated from some bakery products, corn and rice were found to be able to produce territrems. 90% of theA. terreus isolated from bakery products were able to produce territrem A, with a mean of 0.09 ppm, while 80% ofA. terreus isolates produce territrem B with a mean of 0.24 ppm. On the other hand 31.8% of the isolates ofA. terreus from corn were able to produce territrem A with a mean of 0.44 ppm. ConcerningA. terreus isolates from rice, 66.7% were found to produce territrem A, with a mean of 5.28 ppm, and 77.8% of the isolates produced territrem B with a mean of 1.79 ppm.     

Structural response to mutation at a protein-protein interface

We have crystallised three mutants of the barnase-barstar complex in which interactions across the interface have been deleted by simultaneous mutation of both residues involved in the interaction. Each mutant deletes a different type of interaction at the interface: the first complex bnHis102-->Ala-bsTyr29-->Phe (bn, barnase; bs, barstar), deletes a van der Waals packing interaction; the second complex, bnLys27-->Ala-bsThr42-->Ala, deletes a hydrogen bond; the third, bnLys27-->Ala-bsAsp35-->Ala, deletes a long-range charge-charge interaction. The contribution of each of these side-chains to the stability of the complex is known; the coupling energy between the deleted side-chains is also known. Despite each of the double mutants being significantly destabilised compared with the wild-type, the effects of mutation are local. Only small movements in the main-chain surrounding the sites of mutation and some larger movements of neighbouring side-chains are observed in the mutant complexes. The exact response to mutation is context-dependent and for the same mutant can vary depending upon the environment within the crystal. In some double mutant complexes, interfacial pockets, which are accessible to bulk solvent are formed, whereas interfacial cavities which are isolated from bulk solvent, are formed in others. In all double mutants, water molecules fill the created pockets and cavities. These water molecules mimic the deleted side-chains by occupying positions close to the non-carbon atoms of truncated side-chains and re-making many hydrogen bonds made by the truncated side-chains in the wild-type. It remains extremely difficult, however, to correlate energetic and structural responses to mutation because of unknown changes in entropy and entropy-enthalpy compensation.     

Case-control study of leukaemia and non-Hodgkin's lymphoma among children aged 0-4 years living in west Berkshire and north Hampshire health districts.

OBJECTIVE--To investigate the relation between parental employment in the nuclear industry and childhood leukaemia and non-Hodgkin''s lymphoma. DESIGN--Case-control study. SETTING-West Berkshire and Basingstoke and North Hampshire District Health Authorities. SUBJECTS--54 children aged 0-4 years who had leukaemia or non-Hodgkin''s lymphoma diagnosed during 1972-89, who were born in the study area and were resident there when cancer was diagnosed. Six controls were selected for each case: four from hospital delivery registers and two from livebirth registers maintained by the NHS central register. Controls were matched for sex, date of birth (within six months), and area of residence at birth and time of diagnosis. MAIN OUTCOME MEASURES--Parents'' employment by the nuclear industry and exposure to ionising radiation at work. RESULTS--Five (9%) of the 54 cases and 14 (4%) of the 324 controls had fathers or mothers, or both, who had been employed by the nuclear industry (relative risk 2.2, 95% confidence interval 0.6 to 6.9). Nuclear industry employees who work in areas where exposure to radiation is possible are given film badges to monitor their exposure to external penetrating ionising radiation. Three fathers of cases and two fathers of controls (and no mothers of either) had been monitored in this way before their child was conceived (relative risk 9.0, 95% confidence interval 1.0 to 107.8). No father (of a case or control) had accumulated a recorded dose of more than 5 mSv before his child was conceived, and no father had been monitored at any time in the four years before his child was conceived. A dose-response relation was not evident among fathers who had been monitored. CONCLUSIONS--These results suggest that the children of fathers who had been monitored for exposure to external penetrating ionising radiation in the nuclear industry may be at increased risk of developing leukaemia before their fifth birthday. The finding is based on small numbers and could be due to chance. If the relationship is real the mechanisms are far from clear, except that the effect is unlikely to be due to external radiation; the possibility that it could be due to internal contamination by radioactive substances or some other exposure at work should be pursued. The above average rates of leukaemia in the study area cannot be accounted for by these findings.     

Structure and polymorphism of human telomere-associated DNA

We have analyzed the DNA sequences associated with four different human telomeres. Two are members of distinct repeated sequence families which are located mainly but not exclusively at telomeres. Two are unique in the genome, one deriving from the long arm telomere of chromosome 7 and the other from the pseudoautosomal telomere. One telomere-associated repeated sequence has a polymorphic distribution among the chromosome ends, being present at a different combination of ends in different individuals. These data thus identify a new source of human genetic variation and indicate that the canonical features of the organization of telomere-associated DNA are widely conserved in evolution.