Genetic deletions between directly repeated sequences in bacteriophage T7

Summary DNA sequence analysis of genetic deletions in bacteriophage T7 has shown that these chromosomal rearrangements frequently occur between directly repeated DNA sequences. To study this type of spontaneous deletion in more quantitative detail synthetic fragments of DNA, made by hybridizing two complementary oligonucleotides, were introduced into the non-essential T7 gene 1.3 which codes for T7 DNA ligase. This insert blocked synthesis of functional ligase and made the phage that carried an insert unable to form plaques on a host strain deficient in bacterial ligase. The sequence of the insert was designed so that after it is put into the T7 genome the insert is bracketed by direct repeats. Perfect deletion of the insert between the directly repeated sequences results in a wild-type phage. It was found that these deletion events are highly sensitive to the length of the direct repeats at their ends. In the case of 5 bp direct repeats excision from the genome occurred at a frequency of less than 10⁻¹⁰, while this value for an almost identical insert bracketed by 10 bp direct repeats was approximately 10⁻⁶. The deletion events were independent of a hostrecA mutation.     

Genetic characterization of the mei-41 locus in Drosophila melanogaster

Summary The mutagen-sensitive mutant mus(1)104 ^D1 of Drosophila melanogaster maps to a position on the X chromosome very close to the meiotic mutant mei-41 ^D5 . Both mutants have been characterized as mutagen-sensitive and defective in post-replication repair. In the present report we show by complementation studies that mus(1)104 and mus(1)103 are allelic with mei-41. In addition, two reported alleles of mus(1)104 lie between the mei-41 alleles A10 and D5. The size of the mei-41 locus is estimated to be about 0.1 centimorgans (cM). Because several alleles of mei-41 have been shown to reduce recombination and increase meiotic chromosome loss and nondisjunction, mus(1)104 ^D1 females were examined for defects in meiosis. Although there was no evidence for reduced recombination on the second chromosome in homozygous mus(1)104 ^D1 females, heterozygous mus(1)104 ^D1 /mei-41 ^>D5 and mus(1)104 ^D1 /deficiency females showed reduced levels of recombination. However, there was no evidence of an increase in nondijunction in these females.We dedicate this article to the memory of Larry Sandler, who passed away suddenly on February 7, 1987     

Linkage analysis of the myosin heavy chain gene in Dictyostelium discoideum using a mutation generated by homologous recombination

Summary A mutation (mhcA1 in strain HMM) created by insertional gene inactivation was used to map the Dictyostelium discoideum myosin heavy chain gene (mhcA) to linkage group IV. Three phenotypic traits associated with this mutation (slow colony growth, inability of the mutant to develop past aggregation, and the presence of five to ten integrated vector copies) cosegregated as expected for the consequences of a single insertional event. This linkage was confirmed using a restriction fragment length polymorphism. The mhcA1 mutation was recessive to wild type and was nonallelic with mutations at the following loci on linkage group IV: aggJ, aggL, couH, minA, phgB and tsgB. This work demonstrates the ability to apply standard techniques developed for D. discoideum parasexual genetic analyses to mutants generated by transformation, which is of particular relevance to analysis of genes for which no classical mutations or restriction fragment length polymorphisms are available.     

The effect of predation on the structure and invasibility of assembled communities

Summary Fifty four microcosmic communities were assembled over 4 months from a 28-species source pool of phytoplankton using nine different invasion patterns each replicated six times. Three communities from each set of replicates then were invaded with a cladoceran that feeds on phytoplankton. All communities were then treated identically for an additional 4 months. In all nine invasion categories species richness was greater in predated communities. Predation opened communities to invasion by increasing the representation of infrequently sampled species at the expense of more common species. Invasion rate was four times more influential than predation and over eleven times more important than either invasion order or the timing pattern of interspecific arrivals in determining species richness in this system of communitites.     

The contribution of abiotic processes to buried litter decomposition in the northern Chihuahuan desert

Summary Creosobebush (Larrea tridentata) fine litter was treated with either the general biocide HgCl₂ and CuSO₄ or water (controls) and buried 5 cm beneath the soil surface in the northern Chihuahuan Desert. The treated litter showed significantly less mass loss than controls during the three month summer-autumn field study; controls lost about 20% of the original mass while treated litter lost less than 2%. In addition, the total nitrogen content of the control litter increased from an initial concentration of about 14.08 g kg^-1 to 17.62 g kg^-1 dry weight by the end of the study, while treated litter nitrogen content decreased to 13.30 g kg^-1. Results suggest abiotic processes other than leaching have little effect on the decomposition of buried litter in this environment.     

Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods

Of the biogeochemical processes, denitrification has perhaps been the most difficult to study in the field because of the inability to measure the product of the process. The last decade of research, however, has provided both acetylene and¹⁵N based methods as well as undisturbed soil core andin situ soil cover sampling approaches to implementing these methods. All of these methods, if used appropriately, give comparable results. Thus, we now have several methods, each with advantages for particular sites or objectives, that accurately measure denitrification in nature. Because of the general usefulness of the acetylene methods, updated protocols for the following three methods are given: gas-phase recirculation soil cores; static soil cores; and the denitrifying enzyme assay also known as the phase 1 assay. Despite the availability of these and other methods, denitrification budgets remain difficult to accurately establish in most environments because of the high spatial and temporal variability inherent in denitrification. Appropriate analysis of those data includes a distribution analysis of the data, and if highly skewed as is typically the case, the most accurate method to estimate the mean and the population variance is the UMVUE method (uniformly minimum variance unbiased estimator). Geostatistical methods have also been employed to improve spatial and temporal estimates of denitrification. These have occasionally been successful for spatial analysis but in the attempt described here for temporal analysis the approach was not useful.Discussions of the importance of denitrification have always focused on quantifying the process and whether particular measured quantities are judged to be a significant amount of nitrogen. A second line of evidence discussed here is the extant genetic record that results from natural selection. These analysis lead to the conclusion that strong selection for denitrification must currently be occurring, which implies that the process is of general significance in soils.     

A ten-month study of endogenous testosterone levels and behaviour in outdoor-living female rhesus monkeys (Macaca mulatta)

Endogenous testosterone levels were measured in association with sexual, aggressive, and social/affiliative behaviors in 11 outdoor-housed female rhesus monkeys over a ten-month period. Several behaviors (sex directed toward the male, sex received from the male, aggression directed toward the male, submission directed toward the male, submission directed toward the female, and groom another female) were significantly (p<0.05) positively correlated with testosterone in from one to five females. No trends were strong enough across all females to suggest that any of these correlations have species-wide significance. Factor analysis revealed clearcut clusters of behaviors, but elevations in testosterone were not strongly associated with any of these clusters. It is concluded that endogenous testosterone levels have little measurable effect on overt behavior in female rhesus monkeys.     

Evaluation of xylazine hydrochloride as the sole immobilizing agent in moose and caribou--and its subsequent reversal with idazoxan

Xylazine hydrochloride was used as the sole immobilizing agent in moose and caribou. The animals were free-ranging and immobilization was accomplished from a helicopter using powered darts. Following a period of immobilization during which radiotelemetry collars were fitted, the animals were revived using idazoxan (RX 781094) or its methoxy analogue RX 821002. Xylazine was administered at dose rates of approximately 3.0 mg/kg and 5.0 mg/kg to the moose and caribou, respectively. Moose received 430 +/- 27 mg of xylazine and a mean dose of 10 mg idazoxan (RX 781094). Caribou received 485 +/- 30 mg xylazine and a mean dose of 4 mg idazoxan (RX 821002). This technique gave adequate immobilization with rapid recovery of consciousness in both species.