A PIF-dependent recombinogenic signal in the mitochondrial DNA of yeast

From their recombination properties, tandem rho^- mutants of the mitochondrial genome of Saccharomyces cerevisiae were divided into two categories. In crosses between PIF-independent rho^- and rho⁺ strains, the recombination frequency is low and similar in PIF/pif and pif/pif diploids. In crosses between PIF-dependent rho^- and rho⁺ strains, the recombination frequency is stimulated 10-50 times in PIF/pif diploids and is drastically decreased in pif/pif diploids. These results suggest that a recombinogenic signal is present in the mitochondrial (mt) DNA of PIF-dependent rho^- clones. This signal is not recognized in pif mutants. Sequence analysis of a series of small (<300 bp) overlapping tandem rho^- genomes located in the ery region of the 21S rRNA gene led us to identify an essential element of this signal within a 41-bp A+T sequence exhibiting over 26 bp a perfect dyad symmetry. However the recombinogenic signal is not sequence-specific since the sequence described above does not characterize PIF-dependent rho^- clones located in the oli1 region. Our results rather suggest that the recombinogenic signal is related to the topology of rho^- DNA. Denaturated sites in the double helix or cruciform structures elicited by local negative supercoiling might be preferred sites of the initiation of recombination.     

Differential processing of Asn-linked oligosaccharides on pituitary glycoprotein hormones: implications for biologic function

Luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone from pituitary and chorionic gonadotropin from placenta are a family of glycoproteins, each consisting of an and subunit. Within an animal species, the subunit of all four hormones contains the identical amino acid sequence, while each subunit is distinct and confers biologic specificity to the hormone dimer. Despite sharing common subunits, these hormones bear Asn-linked oligosaccharides which differ in structure. Whereas chorionic gonadotropin contains exclusively neutral and sialylated oligosaccharides, the pituitary hormones bear neutral, sialylated, sulfated, and sialylated/sulfated structures. The sulfated oligosaccharides are unique in structure and are more prevalent on certain pituitary hormones, indicating that the synthesis of these unusual oligosaccharides is tightly regulated. The differences in oligosaccharide structures in conjunction with the highly specific endocrine responses elicited by these hormones, suggest an important functional role for the oligosaccharides, such as metabolic clearance, control of hormone response, modulation of hormone potency, and/or intracellular sorting of hormones into separate secretory granules.     

Dependent competing risks: a stochastic process model

Analyses of human mortality data classified according to cause of death frequently are based on competing risk theory. In particular, the times to death for different causes often are assumed to be independent. In this paper, a competing risk model with a weaker assumption of conditional independence of the times to death, given an assumed stochastic covariate process, is developed and applied to cause specific mortality data from the Framingham Heart Study. The results generated under this conditional independence model are compared with analogous results under the standard marginal independence model. Under the assumption that this conditional independence model is valid, the comparison suggests that the standard model overestimates by 4% the effect on life expectancy at age 30 due to the hypothetical elimination of cancer and by 7% the effect for cardiovascular/cerebrovascular disease. By age 80 the overestimates were 11% for cancer and 16% for heart disease. These results suggest the importance of avoiding the marginal independence assumption when appropriate data are available — especially when focusing on mortality at advanced ages.     

Maternal-effect mutations altering the anterior-posterior pattern of the Drosophila embryo

Summary Mutations in seven different maternal-effect loci on the second chromosome of Drosophila melanogaster all cause alterations in the anterior-posterior pattern of the embryo. Mutations in torso (tor) and trunk (trk) delete the anterior- and posterior-most structures of the embryo. At the same time they shift cellular fates which are normally found in the subterminal regions of the embryo towards the poles. Mutations in vasa (vas), valois (vls), staufen (stau) and tudor (tud) cause two embryonic defects. For one they result in absence of polar plasm, polar granules and pole cells in all eggs produced by mutant females. Secondly, embryos developing inside such eggs show deletions of abdominal segments. In addition, embryos derived from staufen mothers lack anterior head structures, embryos derived from valois mothers frequently fail to cellularize properly. Mutations in exuperantia (exu) cause deletions of anterior head structures, similar to torso, trunk and staufen. However in exu, these head structures are replaced by an inverted posterior end which comprises posterior midgut, proctodeal region, and often malpighian tubules.The effects of all mutations can be traced back to the beginning stages of gastrulation, indicating that the alterations in cellular fates have probably taken place by that time. Analysis of embryos derived from double mutant mothers suggests that these three phenotypic groups of mutants interfere with three different, independent pathways. All three pathways seem to act additively on the system which specifies anterior-posterior cellular fates within the egg.     

Effect of maternal dietary exclusion on breast fed infants with eczema: two controlled studies.

Thirty seven breast fed infants with eczema were studied to see whether changes in their mothers'' diets affected their skin condition. Nineteen mothers and babies took part in a double blind crossover trial of exclusion of egg and cows'' milk, and 18 took part in open exclusion of 11 foods followed by double blind challenge to those mothers whose infants seemed to respond. Babies were examined at the beginning and end of each dietary period, and the extent and severity of the rash were given a numerical score. The eczema improved in six infants when their mothers avoided egg and cows'' milk and worsened again when these were reintroduced. Two infants suffered gastrointestinal reactions after maternal ingestion of egg and cows'' milk, one developing colitis. Maternal dietary exclusion seems to benefit some breast fed babies with eczema.     

Immunological studies of Escherichia coli mutants lacking one or two ribosomal proteins

Summary A battery of immunological tests were used to investigate mutants which had been determined as lacking one or two ribosomal proteins on the basis of two-dimensional polyacrylamide gels. Proteins which were confirmed as missing from the ribosome in one or more mutants were large subunit proteins L1, L15, L19, L24, L27, L28, L30 and L33 and small subunit proteins S1, S9, S17 and S20. Cross-reacting material (CRM) was also absent from the post-ribosomal supernatant except in the case of protein S1. Since mutants lacking protein L11 have been previously described, any one of 13 of the 52 ribosomal proteins can be missing. None of these 13 proteins, except S1, can therefore have an indispensable role in ribosome function or assembly. In several mutants in which a protein was not missing but altered, it was present as several moieties of differing charge and size.     

A pterosaurian notarium from the Lower Cretaceous of Brazil

A pterosaur vertebral column consisting of the last cervical vertebra, the first five dorsals fused to a notarium, and the following four dorsal vertebrae, is figured and described from the Aptian Santana Formation of the Chapada do Araripe in northeastern Brazil. The specimen is tentatively referred toSantanadactylus brasilensis de Buisonjé. It is the best preserved and most complete pterosaurian notarium known. Its functional significance is discussed.     

Metabolism of [6-14C]orotate by shoots of Pisum sativum, Phaseolus vulgaris and Lathyrus tingitanus

Incorporation of radioactivity from [6-¹⁴C]orotate into the pyrimidine constituents of shoots of Pisum sativum, Phaseolus vulgaris and Lathyrus tingitanus was examined with special reference to the unusual pyrimidine constituents. With each species, although 80% of the orotate supplied was catabolized to β-alanine, all the pyrimidine derivatives became radioactively labelled. With Pisum, the major part of the radioactivity incorporated into pyrimidines was located in UMP and the uracil derivatives, including the uracilyl amino acids willardiine and isowillardiine. With Phaseolus, UMP and the uracil derivatives were again the major radioactive products; incorporation of radioactivity into 5-ribosyluracil (pseudouridine), which accumulates in Phaseolus tissues, was comparable to the incorporation into orotidine and twice that found in cytidine. Lathyrus incorporated a substantially larger part of the presented [6-¹⁴C] orotate into pyrimidine derivatives than did the other two species. CMP was the most highly radioactive product, followed next by lathyrine and UMP. Surprisingly, 20% of the total radioactivity incorporated into pyrimidines by Lathyrus was located in the pyrimidine amino acid lathyrine. This confirms previous evidence that lathyrine is essentially a product of the orotate pathway. The overall recovery of radioactivity in all three species was 93–95%. The data emphasize the necessity of including the less common pyrimidine constituents, as well as the common ones, in quantitative studies of pyrimidine metabolism in plants.     

Immunological properties of monoclonal antibodies specific for meningococcal polysaccharides: the protective capacity of IgM antibodies specific for polysaccharide group B

Two IgM monoclonal antibodies, MB32 and MB34 specific for meningococcal polysaccharide group B have been raised. Both were detectable by radioimmunoassay and agglutination, but only MB34 was effective in counter immunoelectrophoresis and complement fixation. MB34 was also far more potent than MB32 when tested for passive protection of mice infected with either Neisseria meningitidis group B or Escherichia coli K1. These data demonstrate that group B-specific antibodies do play a protective role in mice infected with these bacteria.