Mitochondria-targeted antioxidant MitoQ ameliorates ischaemia-reperfusion injury in kidney transplantation models

BACKGROUND

Ischaemia-reperfusion (IR) injury makes a major contribution to graft damage during kidney transplantation. Oxidative damage to mitochondria is an early event in IR injury. Therefore, the uptake, safety, and efficacy of the mitochondria-targeted antioxidant MitoQ were investigated in models of transplant IR injury.

METHODS

MitoQ uptake by warm and cooled pairs of pig and declined human kidneys was measured when preserved in cold static storage or by hypothermic machine perfusion. Pairs of pigs' kidneys were exposed to defined periods of warm and cold ischaemia, flushed and stored at 4°C with or without MitoQ (50 nmol/l to 250 µmol/l), followed by reperfusion with oxygenated autologous blood in an ex vivo normothermic perfusion (EVNP). Pairs of declined human kidneys were flushed and stored with or without MitoQ (5-100 µmol/l) at 4°C for 6 h and underwent EVNP with ABO group-matched blood.

RESULTS

Stable and concentration-dependent uptake of MitoQ was demonstrated for up to 24 h in pig and human kidneys. Total blood flow and urine output were significantly greater in pig kidneys treated with 50 µmol/l MitoQ compared with controls (P = 0.006 and P = 0.007 respectively). In proof-of-concept experiments, blood flow after 1 h of EVNP was significantly greater in human kidneys treated with 50 µmol/l MitoQ than in controls (P ≤ 0.001). Total urine output was numerically higher in the 50-µmol/l MitoQ group compared with the control, but the difference did not reach statistical significance (P = 0.054).

CONCLUSION

Mitochondria-targeted antioxidant MitoQ can be administered to ischaemic kidneys simply and effectively during cold storage, and may improve outcomes after transplantation.

Viral inosine triphosphatase: A mysterious enzyme with typical activity, but an atypical function

Plant viruses typically have highly condensed genomes, yet the plant-pathogenic viruses Cassava brown streak virus, Ugandan cassava brown streak virus, and Euphorbia ringspot virus are unusual in encoding an enzyme not yet found in any other virus, the "house-cleaning" enzyme inosine triphosphatase. Inosine triphosphatases (ITPases) are highly conserved enzymes that occur in all kingdoms of life and perform a house-cleaning function by hydrolysing the noncanonical nucleotide inosine triphosphate to inosine monophosphate. The ITPases encoded by cassava brown streak virus and Ugandan cassava brown streak virus have been characterized biochemically and are shown to have typical ITPase activity. However, their biological role in virus infection has yet to be elucidated. Here we review what is known of viral-encoded ITPases and speculate on potential roles in infection with the aim of generating a greater understanding of cassava brown streak viruses, a group of the world's most devastating viruses.

The macrocyclizing protease butelase 1 remains autocatalytic and reveals the structural basis for ligase activity

Plant asparaginyl endopeptidases (AEPs) are expressed as inactive zymogens that perform maturation of seed storage protein upon cleavage-dependent autoactivation in the low-pH environment of storage vacuoles. The AEPs have attracted attention for their macrocyclization reactions, and have been classified as cleavage or ligation specialists. However, we have recently shown that the ability of AEPs to produce either cyclic or acyclic products can be altered by mutations to the active site region, and that several AEPs are capable of macrocyclization given favorable pH conditions. One AEP extracted from Clitoria ternatea seeds (butelase 1) is classified as a ligase rather than a protease, presenting an opportunity to test for loss of cleavage activity. Here, making recombinant butelase 1 and rescuing an Arabidopsis thaliana mutant lacking AEP, we show that butelase 1 retains cleavage functions in vitro and in vivo. The in vivo rescue was incomplete, consistent with some trade-off for butelase 1 specialization toward macrocyclization. Its crystal structure showed an active site with only subtle differences from cleaving AEPs, suggesting the many differences in its peptide-binding region are the source of its efficient macrocyclization. All considered, it seems that either butelase 1 has not fully specialized or a requirement for autocatalytic cleavage is an evolutionary constraint upon macrocyclizing AEPs.

Strategies for the Construction of Cassava Brown Streak Disease Viral Infectious Clones

Cassava brown streak disease (CBSD) has major impacts on yield and quality of the tuberous roots of cassava in Eastern and Central Arica. At least two Potyviridae species cause the disease: Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). Cloned viral genome sequences known as infectious clones (ICs) have been important in the study of other viruses, both as a means of standardising infectious material and characterising viral gene function. IC construction is often technically challenging for Potyviridae due to sequence instability in E. coli. Here, we evaluate three methods for the construction of infectious clones for CBSD. Whilst a simple IC for in vitro transcription was made for UCBSV isolate 'Kikombe', such an approach failed to deliver full-length clones for CBSV isolates 'Nampula' or 'Tanza', necessitating more complex approaches for their construction. The ICs successfully generated symptomatic infection in the model host N. benthamiana and in the natural host cassava. This shows that whilst generating ICs for CBSV is still a technical challenge, a structured approach, evaluating both in vitro and in planta transcription systems should successfully deliver ICs, allowing further study into the symptomology and virulence factors in this important disease complex.

Macrocyclization by asparaginyl endopeptidases

Contents Summary 923 I. Introduction 923 II. Plant AEPs with macrocyclizing ability 924 III. Mechanism of macrocyclization by AEPs 925 IV. Conclusions 927 Acknowledgements 927 References 927 SUMMARY: Plant asparaginyl endopeptidases (AEPs) are important for the post-translational processing of seed storage proteins via cleavage of precursor proteins. Some AEPs also function as peptide bond-makers during the biosynthesis of several unrelated classes of cyclic peptides, namely the kalata-type cyclic peptides, PawS-Derived Peptides and cyclic knottins. These three families of gene-encoded peptides have different evolutionary origins, but all have recruited AEPs for their maturation. In the last few years, the field has advanced rapidly, with the biochemical characterization of three plant AEPs capable of peptide macrocyclization, and insights have been gained from the first AEP crystal structures, albeit mammalian ones. Although the biochemical studies have improved our understanding of the mechanism of action, the focus now is to understand what changes in AEP sequence and structure enable some plant AEPs to perform macrocyclization reactions.

Structural basis of ribosomal peptide macrocyclization in plants

Constrained, cyclic peptides encoded by plant genes represent a new generation of drug leads. Evolution has repeatedly recruited the Cys-protease asparaginyl endopeptidase (AEP) to perform their head-to-tail ligation. These macrocyclization reactions use the substrates amino terminus instead of water to deacylate, so a peptide bond is formed. How solvent-exposed plant AEPs macrocyclize is poorly understood. Here we present the crystal structure of an active plant AEP from the common sunflower, Helianthus annuus. The active site contained electron density for a tetrahedral intermediate with partial occupancy that predicted a binding mode for peptide macrocyclization. By substituting catalytic residues we could alter the ratio of cyclic to acyclic products. Moreover, we showed AEPs from other species lacking cyclic peptides can perform macrocyclization under favorable pH conditions. This structural characterization of AEP presents a logical framework for engineering superior enzymes that generate macrocyclic peptide drug leads.

Most proteins are long, chain-like molecules that have two ends respectively called the N-terminus and C-terminus. However, certain proteins can close on themselves to become circular. This requires a chemical reaction between the N- and C-termini, which creates a strong bond between the two extremities.

To go through this ‘cyclization’ process, a straight protein attaches to a certain type of protease, a class of enzyme that usually cuts proteins into smaller pieces. In plants that are distantly related, the same group of enzymes – called AEPs – has been selected to perform cyclization. Here, Haywood et al. study an AEP enzyme from sunflowers: they identify what about this enzyme’s structure is important to drive the complex chemical reaction that results in the protein being cyclized rather than simply cut.

Using a technique called X-ray crystallography to see the positions of individual atoms in the enzyme, Haywood et al. caught a snapshot of the enzyme. Its structure explained how the enzyme’s shape can guide cyclization. In particular, the part of the enzyme that binds to the proteins, the active site, was relatively flat and open, but also flexible: this helped the N and C-termini react with each other and close the protein. Further experiments artificially mutated specific areas of the enzyme, which helped determine exactly which elements guide this succession of chemical reactions.

The activity of AEPs is influenced by their local environment, such as acidity. In fact, Haywood et al. showed that certain AEPs, which do not normally carry out cyclization, can start performing this role when exposed to a different level of acidity.

The pharmaceutical industry is increasingly interested in circular proteins, as these are stable, easily used by the body, and can be genetically customized to act only on specific targets. If the cyclization process is better understood, and then harnessed, new drug compounds could be produced.

Two proteins for the price of one: Structural studies of the dual-destiny protein preproalbumin with sunflower trypsin inhibitor-1

Seed storage proteins are both an important source of nutrition for humans and essential for seedling establishment. Interestingly, unusual napin-type 2S seed storage albumin precursors in sunflowers contain a sequence that is released as a macrocyclic peptide during post-translational processing. The mechanism by which such peptides emerge from linear precursor proteins has received increased attention; however, the structural characterization of intact precursor proteins has been limited. Here, we report the 3D NMR structure of the Helianthus annuus PawS1 (preproalbumin with sunflower trypsin inhibitor-1) and provide new insights into the processing of this remarkable dual-destiny protein. In seeds, PawS1 is matured by asparaginyl endopeptidases (AEPs) into the cyclic peptide SFTI-1 (sunflower trypsin inhibitor-1) and a heterodimeric 2S albumin. The structure of PawS1 revealed that SFTI-1 and the albumin are independently folded into well-defined domains separated by a flexible linker. PawS1 was cleaved in vitro with recombinant sunflower HaAEP1 and in situ using a sunflower seed extract in a way that resembled the expected in vivo cleavages. Recombinant HaAEP1 cleaved PawS1 at multiple positions, and in situ, its flexible linker was removed, yielding fully mature heterodimeric albumin. Liberation and cyclization of SFTI-1, however, was inefficient, suggesting that specific seed conditions or components may be required for in vivo biosynthesis of SFTI-1. In summary, this study has revealed the 3D structure of a macrocyclic precursor protein and provided important mechanistic insights into the maturation of sunflower proalbumins into an albumin and a macrocyclic peptide.

Evidence for Ancient Origins of Bowman-Birk Inhibitors from Selaginella moellendorffii

Bowman-Birk Inhibitors (BBIs) are a well-known family of plant protease inhibitors first described 70 years ago. BBIs are known only in the legume (Fabaceae) and cereal (Poaceae) families, but peptides that mimic their trypsin-inhibitory loops exist in sunflowers (Helianthus annuus) and frogs. The disparate biosynthetic origins and distant phylogenetic distribution implies these loops evolved independently, but their structural similarity suggests a common ancestor. Targeted bioinformatic searches for the BBI inhibitory loop discovered highly divergent BBI-like sequences in the seedless, vascular spikemoss Selaginella moellendorffii Using de novo transcriptomics, we confirmed expression of five transcripts in S. moellendorffii whose encoded proteins share homology with BBI inhibitory loops. The most highly expressed, BBI3, encodes a protein that inhibits trypsin. We needed to mutate two lysine residues to abolish trypsin inhibition, suggesting BBI3's mechanism of double-headed inhibition is shared with BBIs from angiosperms. As Selaginella belongs to the lycopod plant lineage, which diverged ∼200 to 230 million years before the common ancestor of angiosperms, its BBI-like proteins imply there was a common ancestor for legume and cereal BBIs. Indeed, we discovered BBI sequences in six angiosperm families outside the Fabaceae and Poaceae. These findings provide the evolutionary missing links between the well-known legume and cereal BBI gene families.

The geographic distribution and ecological preferences of the American dog tick, Dermacentor variabilis (Say), in the U.S.A

Equine piroplasmosis (EP), caused by two parasitic organisms, Theileria equi and Babesia caballi, is a tick-borne disease of recent concern in horses in the U.S.A. Outbreaks of EP have been detected in Florida, Missouri, Kansas and Texas. In 2009, EP transmission in Texas occurred through the adults of two tick species, Amblyomma mixtum [formerly known as Amblyomma cajennense (Fabricius, 1787)] Koch (Ixodida: Ixodidae) and Dermacentor variabilis (Say) (Ixodida: Ixodidae), the American dog tick (ADT). In this study, we developed a continent-scale map for the distribution of the EP vector species D. variabilis, using a presence-only modelling approach to assess the habitat preferences of this tick. We used identification records from our tick geodatabase of locations in which the presence of the ADT had been noted. The potential distribution of the ADT in the U.S.A. was estimated from environmental factors using the maximum entropy approach based on localities in which there is a high probability of occurrence according to habitat suitability. Elevation and temperature were found to be biologically significant environmental variables influencing the presence of this tick species. Properly designed and constructed probability surfaces using maximum entropy offer one useful approach to the mapping of distribution ranges of tick species based on suitable habitat in the U.S.A.

Non-protein components of the cell surface of Staphylococcus aureus

1. pH-mobility curves of various laboratory strains of Staphylococcus aureus are non-sigmoid in shape, and all pass through a maximum value in the range pH4-5. 2. The maxima in the curves are not due to incomplete washing of the cells, adsorption of buffer components or irreversible surface damage. 3. Mild oxidation of the cell-surface teichoic acid with sodium metaperiodate gives cells that have typical sigmoid pH-mobility curves, characteristic of either a simple carboxyl surface or a mixed carboxyl-amino surface. 4. The results are discussed in terms of a pH-dependent change in the configuration of the teichoic acid molecules at the surface.

Lipophilic triphenylphosphonium cations as tools in mitochondrial bioenergetics and free radical biology

Lipophilic phosphonium cations were first used to investigate mitochondrial biology by Vladimir Skulachev and colleagues in the late 1960s. Since then, these molecules have become important tools for exploring mitochondrial bioenergetics and free radical biology. Here we review why these molecules are useful in mitochondrial research and outline some of the ways in which they are now being utilized.

Using mitochondria-targeted molecules to study mitochondrial radical production and its consequences

The production of ROS (reactive oxygen species) by the mitochondrial respiratory chain contributes to a range of pathologies, including neurodegenerative diseases, ischaemia/reperfusion injury and aging. There are also indications that mitochondrial ROS production plays a role in damage response and signal transduction pathways. To unravel the role of mitochondrial ROS production in these processes, we have developed a range of mitochondria-targeted probe molecules. Covalent attachment of a lipophilic cation leads to their accumulation into mitochondria, driven by the membrane potential. Molecules developed so far include antioxidants designed to intercept mitochondrial ROS and reagents that specifically label mitochondrial thiol proteins. Here we outline how mitochondrial ROS formation and its consequences can be investigated using these probes.

An enzootic transmission cycle of Lyme borreliosis spirochetes in the southeastern United States

Lyme borreliosis, or Lyme disease (LD), is a tick-borne zoonotic infection of biomedical significance, caused by Borrelia burgdorferi sensu lato (s.l.) spirochetes and transmitted by Ixodes species ticks. It usually circulates among wildlife vertebrate reservoirs and vector ticks but may infect humans, causing multisystem problems. In far western and northern North America, the host reservoirs, tick vectors, and genospecies of Borrelia are well known but not so in the southern U.S., where there is controversy as to the presence of "true" LD. Here we report the presence of the LD spirochete B. burgdorferi sensu stricto (s.s.) and Borrelia bissettii, three main reservoir hosts, and two enzootic tick vectors in the southeastern U.S. The two enzootic tick vectors, Ixodes affinis and Ixodes minor, rarely bite humans but are more important than the human biting "bridge" vector, Ixodes scapularis, in maintaining the enzootic spirochete cycle in nature. We also report extraordinary longevities and infections in the reservoir rodents Peromyscus gossypinus, Sigmodon hispidus, and Neotoma floridana.

Host associations of ticks parasitizing rodents at Borrelia burgdorferi enzootic sites in South Carolina

A total of 237 rodents was collected in 4 regions of South Carolina from July 1994 through December 1995. Eight species were collected, including cotton mouse, hispid cotton rat, eastern woodrat, marsh rice rat, white-footed mouse, eastern harvest mouse, golden mouse, and black rat. Of the 1,514 ticks recovered from these hosts, Ixodes minor Neumann, including larvae, nymphs, and adults, was the most abundant species, representing 54% of the total. Only immature stages of other tick species were found, including larvae and nymphs of Dermacentor variabilis (Say), Amblyomma maculatum Koch, Ixodes affinis Neumann, and Ixodes scapularis Say. All 5 tick species parasitized cotton mice, cotton rats, and woodrats, which were the most important small mammal hosts for ticks at the localities studied. Rice rats were hosts of A. maculatum, D. variabilis, and L. minor. Amblyomma maculatum was more strongly associated with cotton rats than other rodent species. Ixodes scapularis was most strongly associated with cotton mice, and I. minor was more strongly associated with both woodrats and cotton mice than other species of rodents. Ixodes minor parasitized hosts in the Coastal Zone only, where among spirochete-infected hosts, it was present in significantly greater numbers than other ticks. Furthermore, I. minor was the only tick species that showed a statistically significant positive association with spirochetal infection in rodents. More I. affinis parasitized spirochete-infected hosts than I. scapularis, but fewer than I. minor. The findings discussed herein provide evidence that implicates I. minor as the possible primary enzootic vector of the Lyme disease spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt and Brenner in the Coastal Zone of South Carolina. They also indicate that the high level of B. burgdorferi infection in rodents from this region may be a function of the combined involvement of I. minor, I. affinis, and I. scapularis in the enzootic transmission of the spirochete.

Borrelia lonestari infection after a bite by an Amblyomma americanum tick

Erythematous rashes that are suggestive of early Lyme disease have been associated with the bite of Amblyomma americanum ticks, particularly in the southern United States. However, Borrelia burgdorferi, the causative agent of Lyme disease, has not been cultured from skin biopsy specimens from these patients, and diagnostic serum antibodies usually have not been found. Borrelia lonestari sp nov, an uncultured spirochete, has been detected in A. americanum ticks by DNA amplification techniques, but its role in human illness is unknown. We observed erythema migrans in a patient with an attached A. americanum tick. DNA amplification of the flagellin gene flaB produced B. lonestari sequences from the skin of the patient that were identical to those found in the attached tick. B. lonestari is a probable cause of erythema migrans in humans.

Isolation, cultivation, and characterization of Borrelia burgdorferi from rodents and ticks in the Charleston area of South Carolina

Twenty-eight Borrelia burgdorferi isolates from the Charleston, S.C., area are described. This represents the first report and characterization of the Lyme disease spirochete from that state. The isolates were obtained from December 1994 through December 1995 from the tick Ixodes scapularis, collected from vegetation, and from the rodents Peromyscus gossypinus (cotton mouse), Neotoma floridana (eastern wood rat), and Sigmodon hispidus (cotton rat). All isolates were screened immunologically by indirect immunofluorescence with monoclonal antibodies to B. burgdorferi-specific outer surface protein A (OspA) (antibodies H5332 and H3TS) and B. burgdorferi-specific OspB (antibodies H6831 and H614), a Borrelia (genus)-specific antiflagellin antibody (H9724), Borrelia hermsii-specific antibodies (H9826 and H4825), and two polyclonal antibodies (one to Borrelia species and another to B. burgdorferi). Six of the isolates were analyzed by exposing Western blots to monoclonal antibodies H5332, H3TS, H6831, and H9724. All isolates were also analyzed by PCR with five pairs of primers known to amplify selected DNA target sequences specifically reported to be present in the reference strain, B. burgdorferi B-31. The protein profiles of six of the isolates (two from ticks, one from a cotton mouse, two from wood rats, and one from a cotton rat) also were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We conclude that the 28 Charleston isolates are B. burgdorferi sensu stricto based on their similarities to the B. burgdorferi B-31 reference strain.

Closing rural hospitals in Saskatchewan: on the road to wellness?

Rising health care costs at a time of economic stagnation, federal cutbacks to Medicare, and an obsession with budget deficits at all levels of government have contributed to a sense of urgency to reform the Canadian health care system. Accompanying these economic and political motivations for reform, has been a shift in our understanding of health and well-being that lays less emphasis on the institutionalization and medicalization of health care. As part of its wellness approach to health, the Saskatchewan government in 1992 announced the closure and conversion of 52 small rural hospitals to wellness centres as part of a shift from institutional care to community based care. While the health costs and benefits of this shift are contested, the paradox is that closing rural hospitals may have unrealized health and social costs because of the psychological and community importance of hospitals to the meaning of place. This paper begins with a review of the meaning and importance of local institutions for communities. It is clear from this starting point that the debate about the economic and health benefits and costs of rural hospital closures is a limited basis for understanding hospital closures. Finally, the history of Saskatchewan hospitals and a narrative of the recent closures of rural hospitals drawn from a sampling of provincial newspapers and oral discussions highlights the need to understand the hospital closure in terms of its impact on health irrespective of the medical impacts.

Quantitation and origin of the mitochondrial membrane potential in human cells lacking mitochondrial DNA

Mammalian mitochondrial DNA (mtDNA) encodes 13 polypeptide components of oxidative phosphorylation complexes. Consequently, cells that lack mtDNA (termed rho degrees cells) cannot maintain a membrane potential by proton pumping. However, most mitochondrial proteins are encoded by nuclear DNA and are still imported into mitochondria in rho degrees cells by a mechanism that requires a membrane potential. This membrane potential is thought to arise from the electrogenic exchange of ATP4- for ADP3- by the adenine nucleotide carrier. An intramitochondrial ATPase, probably an incomplete FoF1-ATP synthase lacking the two subunits encoded by mtDNA, is also essential to ensure sufficient charge flux to maintain the potential. However, there are considerable uncertainties about the magnitude of this membrane potential, the nature of the intramitochondrial ATPase and the ATP flux required to maintain the potential. Here we have investigated these factors in intact and digitonin-permeabilized mammalian rho degrees cells. The adenine nucleotide carrier and ATP were essential, but not sufficient to generate a membrane potential in rho degrees cells and an incomplete FoF1-ATP synthase was also required. The maximum value of this potential was approximately 110 mV in permeabilized cells and approximately 67 mV in intact cells. The membrane potential was eliminated by inhibitors of the adenine nucleotide carrier and by azide, an inhibitor of the incomplete FoF1-ATP synthase, but not by oligomycin. This potential is sufficient to import nuclear-encoded proteins but approximately 65 mV lower than that in 143B cells containing fully functional mitochondria. Subfractionation of rho degrees mitochondria showed that the azide-sensitive ATPase activity was membrane associated. Further analysis by blue native polyacrylamide gel electrophoresis (BN/PAGE) followed by activity staining or immunoblotting, showed that this ATPase activity was an incomplete FoF1-ATPase loosely associated with the membrane. Maintenance of this membrane potential consumed about 13% of the ATP produced by glycolysis. This work has clarified the role of the adenine nucleotide carrier and an incomplete FoF1-ATP synthase in maintaining the mitochondrial membrane potential in rho degrees cells.

The Borrelia burgdorferi 37-kilodalton immunoblot band (P37) used in serodiagnosis of early lyme disease is the flaA gene product

The 37-kDa protein (P37) of Borrelia burgdorferi is an antigen that elicits an early immunoglobulin M (IgM) antibody response in Lyme disease patients. The P37 gene was cloned from a B. burgdorferi genomic library by screening with antibody from a Lyme disease patient who had developed a prominent humoral response to the P37 antigen. DNA sequence analysis of this clone revealed the identity of P37 to be FlaA, an outer sheath protein of the periplasmic flagella. Recombinant P37 expression was accomplished in Escherichia coli by using a gene construct with the leader peptide deleted and fused to a 38-kDa E. coli protein. The recombinant antigen was reactive in IgM immunoblots using serum samples from patients clinically diagnosed with early Lyme disease that had been scored positive for B. burgdorferi anti-P37 reactivity. Lyme disease patient samples serologically negative for the B. burgdorferi P37 protein did not react with the recombinant. Recombinant P37 may be a useful component of a set of defined antigens for the serodiagnosis of early Lyme disease. This protein can be utilized as a marker in diagnostic immunoblots, aiding in the standardization of the present generation of IgM serologic tests.

Decreased ATP synthesis is phenotypically expressed during increased energy demand in fibroblasts containing mitochondrial tRNA mutations

Mutations in the tRNA genes of mitochondrial DNA (mtDNA) cause the debilitating MELAS (mitochondrial, myopathy, encephalopathy, lactic acidosis and stroke-like episodes) and MERRF (myoclonic epilepsy and ragged-red fibres) syndromes. These mtDNA mutations affect respiratory chain function, apparently without decreasing cellular ATP concentration [Moudy et al. (1995) PNAS, 92, 729-733]. To address this issue, we investigated the role of mitochondrial ATP synthesis in fibroblasts from MELAS and MERRF patients. The maximum rate of mitochondrial ATP synthesis was decreased by 60-88%, as a consequence of the decrease in the proton electrochemical potential gradient of MELAS and MERRF mitochondria. However, in quiescent fibroblasts neither ATP concentration or the ATP/ADP ratio was affected by the lowered rate of ATP synthesis. We hypothesized that the low ATP demand of quiescent fibroblasts masked the mitochondrial ATP synthesis defect and that this defect might become apparent during higher ATP use. To test this we simulated high energy demand by titrating cells with gramicidin, an ionophore that stimulates ATP hydrolysis by the plasma membrane Na+/K+-ATPase. We found a threshold gramicidin concentration in control cells at which both the ATP/ADP ratio and the plasma membrane potential decreased dramatically, due to ATP demand by the Na+/K+-ATPase outstripping mitochondrial ATP synthesis. In MELAS and MERRF fibroblasts the corresponding threshold concentrations of gramicidin were 2-20-fold lower than those for control cells. This is the first demonstration that cells containing mtDNA mutations are particularly sensitive to increased ATP demand and this has several implications for how mitochondrial dysfunction contributes to disease pathophysiology. In particular, the increased susceptibility to plasma membrane depolarization will render neurons with dysfunctional mitochondria susceptible to excitotoxic cell death.

Bioenergetic consequences of accumulating the common 4977-bp mitochondrial DNA deletion

Mutations and deletions in mitochondrial DNA (mtDNA) lead to a number of human diseases characterized by neuromuscular degeneration. Accumulation of truncated mtDNA molecules (delta-mtDNA) lacking a specific 4977-bp fragment, the common deletion, leads to three related mtDNA diseases: Pearson's syndrome; Kearns-Sayre syndrome; and chronic progressive external ophthalmoplegia (CPEO). In addition, the proportion of delta-mtDNA present increases with age in a range of tissues. Consequently, there is considerable interest in the effects of the accumulation of delta-mtDNA on cell function. The 4977-bp deletion affects genes encoding 7 polypeptide components of the mitochondrial respiratory chain, and 5 of the 22 tRNAs necessary for mitochondrial protein synthesis. To determine how the accumulation of delta-mtDNA affects oxidative phosphorylation we constructed a series of cybrids by fusing a human osteosarcoma cell line depleted of mtDNA (rho0) with enucleated skin fibroblasts from a CPEO patient. The ensuing cybrids contained 0-86% delta-mtDNA and all had volumes, protein contents, plasma-membrane potentials and mitochondrial contents similar to those of the parental cell line. The bioenergetic consequences of accumulating delta-mtDNA were assessed by measuring the mitochondrial membrane potential, rate of ATP synthesis and ATP/ADP ratio. In cybrids containing less than 50-55% delta-mtDNA, these bioenergetic functions were equivalent to those of cybrids with intact mtDNA. However, once the proportion of delta-mtDNA exceeded this threshold, the mitochondrial membrane potential, rate of ATP synthesis, and cellular ATP/ADP ratio decreased. These bioenergetic deficits will contribute to the cellular pathology associated with the accumulation of delta-mtDNA in the target tissues of patients with mtDNA diseases.

High-Resolution Study of the Near-Infrared A2Pi1/2-X2Sigma+ Transition of YS

A high-resolution excitation spectrum of gaseous YS has been recorded by laser excitation spectroscopy in a supersonic molecular beam. The YS molecules were produced by the reaction of laser-ablated yttrium atoms with CS2. The band of the A 2Pi1/2-X 2Sigma+ transition near 750 nm was rotationally analyzed, and a set of molecular constants is given for both electronic states. Copyright 1998 Academic Press.

First isolation and cultivation of Borrelia burgdorferi sensu lato from Missouri

Five Borrelia burgdorferi sensu lato isolates from Missouri are described. This represents the first report and characterization of such isolates from that state. The isolates were obtained from either Ixodes dentatus or Amblyomma americanum ticks that had been feeding on cottontail rabbits (Sylvilagus floridanus) from a farm in Bollinger County, Mo., where a human case of Lyme disease had been reported. All isolates were screened immunologically by indirect immunofluorescence by using monoclonal antibodies to B. burgdorferi-specific outer surface protein A (OspA) (antibodies H3TS and H5332), B. burgdorferi-specific OspB (antibody H6831), Borrelia (genus)-specific antiflagellin (antibody H9724), and Borrelia hermsii-specific antibody (antibody H9826). Analysis of the isolates also involved a comparison of their protein profiles by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Finally, the isolates were analyzed by PCR with six pairs of primers known to amplify selected DNA target sequences specifically found in the reference strain B. burgdorferi B-31. Although some genetic variability was detected among the five isolates as well as between them and the B-31 strain, enough similarities were found to classify them as B. burgdorferi sensu lato.

Ticks, Lyme disease spirochetes, trypanosomes, and antibody to encephalitis viruses in wild birds from coastal Georgia and South Carolina

Ticks and blood samples were collected from wild birds mist-netted on St. Catherine's Island, Georgia, and at the Wedge Plantation in coastal South Carolina in 1994 and 1995. Immature stages of 5 species of ixodid ticks were recovered from 10 of 148 (7%) birds belonging to 6 species in Georgia, whereas 6 ixodid species were recovered from 45 of 259 (17%) birds representing 10 avian species in South Carolina. Borrelia burgdorferi sensu lato was isolated from 27 of 120 (23%) screened ticks (Ixodes scapularis and Ixodes minor) recovered from South Carolina birds, but from none of 16 screened ticks removed from Georgia birds. This spirochete was also isolated from 1 of 97 (1%) birds in South Carolina. In 1995, neither eastern equine encephalitis (EEE) virus nor St. Louis encephalitis (SLE) virus was isolated from any of 218 bird sera screened, but serum neutralizing antibodies were found to EEE virus in 4 of 121 (3%) sera and to SLE virus in 2 of 121 (2%) sera from South Carolina. No antibody to either virus was detected in 51 avian sera screened from Georgia. Trypanosomes (probably Trypanosoma avium) were isolated from 1 of 51 (2%) birds from Georgia and from 13 of 97 (13%) birds from South Carolina. Our data suggest that some wild birds may be reservoir hosts for the Lyme disease spirochete and for encephalitis viruses in coastal Georgia and South Carolina and that migrating birds can disperse immature ticks infected with B. burgdorferi.

Vitellogenin and ecdysteroid titers in Ixodes scapularis during vitellogenesis

Ecdysteroids are the only hormones unequivocally identified thus far in ticks. We found a positive correlation between ecdysteroid concentration and vitellogenin synthesis in female Ixodes scapularis. Vitellogenin (Vg) synthetic activity was measured by an in vitro assay for Vg, involving incubations of the fat body with 35S-methionine and immunoprecipitation collected on a solid-phase matrix, protein A. Vitellogenin synthetic activity in the fat body was undetectable in unfed females but was detected after tick attachment to the host. Vitellogenin production in the fat body remained low from attachment until 2 days prior to detachment from the host. Vitellogenin synthesis in the fat body peaked 2 days after detachment and declined to a level 2-3 times above background from 6 days after dropping from the host through oviposition. A peak of ecdysteroids in females 6 days after attachment preceded an increasing rate of Vg synthesis, suggesting a positive correlation between these parameters. Ecdysone and 20-hydroxyecdysone, the 2 major ecdysteroids present during vitellogenesis, could not be detected in females prior to feeding or 2 days after attachment to the host; however, concentrations began to increase 4 days after attachment, peaked during rapid engorgement, and subsequently declined.

Purification and partial characterization of vitellin from the black-legged tick, Ixodes scapularis

Vitellin from the black-legged tick, Ixodes scapularis, was purified from eggs using gel filtration and ion exchange chromatography. The purified protein had a native molecular mass of 480 kDa. Under reducing conditions (sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SDS-PAGE), vitellin was composed of seven polypeptides each at 154, 135, 87, 78, 67, 64 and 35 kDa. The isoelectric point was pH 6.9 and absorption maxima for the yolk protein were 280 and 400 nm. As in other ticks, vitellin from I. scapularis is also a hemoglycolipoprotein. Carbohydrates detected in vitellin were predominantly mannose with a small amount of N-acetylglucosamine. Lipids detected by thin layer chromatography (TLC) were triglycerides, free fatty acids, and cholesterol. Phospholipids associated with vitellin were phosphatidylethanolamine and phosphatidylcholine. Polyclonal serum produced in rabbits recognized vitellin from the eggs and ovaries, and vitellogenin from the hemolymph and fat body in reproductive females. This is the first report on the characterization of yolk proteins from a prostriate tick.

The effect on mitochondrial function of the tRNA Ser(UCN)/COI A7445G mtDNA point mutation associated with maternally-inherited sensorineural deafness

An A to G point mutation at nucleotide position 7445 in the mitochondrial DNA genome is associated with maternally-inherited sensorineural deafness in two separate human pedigrees. To determine whether this point mutation [tRNA(SER)UCN)/COI A7445G] led to sensorineural deafness by affecting cellular energy metabolism we investigated the bioenergetic function of mitochondria in lymphoblastoid cultures established from these patients. Even though essentially all of the mitochondrial DNA in these cells contained the mutation at nucleotide position 7445, there was no effect on a number of mitochondrial bioenergetic functions (mitochondrial content, membrane potential in both intact and digitonin-permeabilised cells, cellular ATP/ADP ratios and respiratory enzyme activity) when compared with control cells. The implications of these findings for both the aetiology of the sensorineural deafness associated with the A7445G mtDNA mutation, and the role of bioenergetic defects in mitochondrial DNA diseases in general are discussed.

Unusual strain of Borrelia burgdorferi isolated from Ixodes dentatus in central Georgia

A new, unusual spirochete was cultured in Barbour-Stoenner-Kelly (BSK II) medium from the midgut and other tissues of the tick Ixodes dentatus. The tick was collected from leaf litter in an oak-pine wood lot in Bibb County approximately 7.2 km from Macon in central Georgia during February 1993. Characterization by indirect immunofluorescence using 5 murine monoclonal antibodies, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole spirochetal lysates, and by polymerase chain reaction assay for several known DNA target sequences indicates that the spirochete is Borrelia burgdorferi sensu lato. It is genetically different from the B-31 reference strain of B. burgdorferi sensu stricto that is typical of strains causing Lyme borreliosis in North America. Range of infectivity and pathogenesis of the Bibb County isolate (BC-1) are unknown but being investigated. The BC-1 strain is the first B. burgdorferi isolate from I. dentatus in the southeastern United States (I. dentatus is not the common vector for Lyme borreliosis in humans). Additionally, the collection site was approximately 322 km from the Atlantic coast, far distant from where most B. burgdorferi isolates have been obtained.

Vitellogenin concentrations in the haemolymph and ovaries of Ixodes scapularis ticks during vitellogenesis

The vitellogenin and vitellin concentrations in the haemolymph and ovaries of Ixodes scapularis females were determined using a double sandwich enzyme-linked immunosorbent assay. The level of vitellogenin in the haemolymph began to increase just prior to tick detachment from the host and continued to increase until 2 days after detachment. There was a slight decrease in the vitellogenin level 4 days after detachment, but a second peak was observed approximately 5 days after oviposition. Subsequent to oviposition, the vitellogenin levels in the haemolymph quickly decreased. The concentration of vitellogenin in the haemolymph ranged from 1.55 to 11.48 micrograms microliters-1 during the period after dropping from the host through oviposition. The concentration of vitellin in the ovaries began to increase as the female began rapid engorgement (0.03 mg per female) and declined after oviposition (0.1 mg per female).

Altered mitochondrial function in fibroblasts containing MELAS or MERRF mitochondrial DNA mutations

A number of human diseases are caused by inherited mitochondrial DNA mutations. Two of these diseases, MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) and MERRF (myoclonic epilepsy and ragged-red fibres), are commonly caused by point mutations to tRNA genes encoded by mitochondrial DNA. Here we report on how these mutations affect mitochondrial function in primary fibroblast cultures established from a MELAS patient containing an A to G mutation at nucleotide 3243 in the tRNA(Leu(UUR) gene and a MERRF patient containing an A to G mutation at nucleotide 8344 in the tRNA(Lys) gene. Both mitochondrial membrane potential and respiration rate were significantly decreased in digitonin-permeabilized MELAS and MERRF fibroblasts respiring on glutamate/malate. A similar decrease in mitochondrial membrane potential was found in intact MELAS and MERRF fibroblasts. The mitochondrial content of these cells, estimated by stereological analysis of electron micrographs and from measurement of mitochondrial marker enzymes, was similar in control, MELAS and MERRF cells. Therefore, in cultured fibroblasts, mutation of mitochondrial tRNA genes leads to assembly of bioenergetically incompetent mitochondria, not to an alteration in their amount. However, the cell volume occupied by secondary lysosomes and residual bodies in the MELAS and MERRF cells was greater than in control cells, suggesting increased mitochondrial degradation in these cells. In addition, fibroblasts containing mitochondrial DNA mutations were 3-4-fold larger than control fibroblasts. The implications of these findings for the pathology of mitochondrial diseases are discussed.

Natural occurrence and characterization of the Lyme disease spirochete, Borrelia burgdorferi, in cotton rats (Sigmodon hispidus) from Georgia and Florida

This is the first report of natural infection by Borrelia burgdorferi in the cotton rat Sigmodon hispidus. Nine B. burgdorferi isolates were obtained from ear tissues, urinary bladders, or both, by culturing tissues in BSKII medium. The rat from which the SI-3 isolate was cultured was from the same site (Sapelo Island, Georgia) as an infected cotton mouse Peromyscus gossypinus and Ixodes scapularis tick reported previously. The 8 B. burgdorferi isolates from rats in Florida included 1 (AI-1) from Amelia Island, 1 (FD-1) from Faver-Dykes State Park, and 6 (MI-3 through MI-8) from Merritt Island. The distance between Sapelo Island and Merritt Island is approximately 400 km. All B. burgdorferi isolates were characterized by indirect immunofluorescence using monoclonal antibodies to OspA (H3TS, H5332) and OspB (H5TS, H6831), polymerase chain reaction detection of specific B. burgdorferi B-31 DNA target sequences (ospA, fla, and a random chromosomal sequence), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of spirochetal proteins. The phenotypic and genotypic characteristics of the isolates are discussed, as well as the probable importance of the cotton rat as a reservoir for B. burgdorferi in the southern United States.

Reaction of human chymase with reactive site variants of alpha 1-antichymotrypsin. Modulation of inhibitor versus substrate properties

Inhibition of human chymase by alpha 1-antichymotrypsin produces 3.5 mol of degraded inhibitor for every mol of chymase inhibited, resulting in a stoichiometry of inhibition (SI) of 4.5. In the present study, the substrate versus inhibitor properties of this reaction were examined further using wild type and mutant recombinant antichymotrypsins (rACT). Titration of chymase hydrolytic activity with rACT-L358 (wild type) and reactive site (P1) variants of ACT, L358W, L358M, and L358F revealed that the SI was sensitive to P1 residue replacements. SI values increased in the order of Trp < Met < Leu < Phe where SI values were 1.5, 2, 4, and 7, respectively. Chymase inhibitor complex and cleaved inhibitor were demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis for all variants; the relative intensities of each band were consistent with SI values established by titration. NH2-terminal sequence analyses of the products formed in the reaction of chymase with rACT-L358F indicated that the P1-P1' bond was the primary site of cleavage resulting in the hydrolysis and inactivation of this variant. The apparent second-order rate constant for chymase inhibition (k'/[I]) by rACT also was affected by P1 substitution. k'/[I] values increased in an order opposite that obtained for SI values (Phe < Leu < Met < Trp). The reactive loop mutant (rACT-P3P3') produced by replacing the reactive site region of ACT (Thr356-Val361) with that of alpha 1-proteinase inhibitor (Ile356-Pro361) revealed a different reaction pattern. Although its SI was near 1, the value for k'/[I] was the lowest among variants. rACT-L358R, another P1 variant, did not inhibit chymase. These results are evaluated with respect to the substrate preferences of human chymase and with respect to partitioning schemes proposed to explain SI values greater than 1.

Developmental and gender differences in the relationship of behavior pattern to heart rate reactivity between two teenage samples

The Type A Behavior Pattern was assessed for 122 teenagers from two age-groups. Subjects had their heart rate measured during rest and presentation of a mental arithmetic stressor under timed and competitive conditions. Data were analyzed to determine whether sex, age, task performance, and behavior pattern predicted the degree of heart rate reactivity shown by these children. Although there were no significant main effects for behavior pattern, sex, or age, there was a significant interaction among age, sex, and behavior pattern. It is suggested that the two age groups of teenagers sampled here differ in the relationships they show between behavior pattern and heart rate reactivity. This result challenges some previous assumptions with regard to the homogeneity of teenagers on this issue.

Isolation and transmission of the Lyme disease spirochete from the southeastern United States

The isolation of the Lyme disease spirochete (Borrelia burgdorferi) from the southeastern United States is reported. Three isolates, two from cotton mice (Peromyscus gossypinus) and one from the black-legged tick (Ixodes scapularis), were recovered from Sapelo Island, Georgia, in July and September 1991. The spirochetes were characterized by indirect fluorescent antibody assay using a battery of five monoclonal antibodies, by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) of whole cell lysates, and by the polymerase chain reaction (PCR) assay using primers for three DNA target sequences found in B. burgdorferi reference strain B-31. Transmission experiments indicate that the three Georgia isolates can infect experimentally inoculated hamsters and mice. Tick transmission of one of the isolates has been attempted so far; I. scapularis transmitted isolate SI-1 from hamsters to mice, but the lone-star tick, Amblyomma americanum, did not.

Conspecificity of the ticks Ixodes scapularis and I. dammini (Acari: Ixodidae)

Reciprocal crosses between Ixodes dammini Spielman, Clifford, Piesman & Corwin from Massachusetts and Ixodes scapularis Say from Georgia produced offspring through the F3 generation when the experiment was discontinued. Reciprocal I. dammini x Ixodes pacificus Cooley & Kohls (California) and I. scapularis x I. pacificus crosses produced F1 progeny; however, all progeny were sterile. Assortative mating experiments between I. dammini and I. scapularis indicated that males and females of both species mated with the opposite sex of heterospecific or conspecific ticks when there was a choice. Conventional discriminant analysis of morphometric measurements of ticks from Georgia, North Carolina, Maryland, Massachusetts, and two populations of F1 hybrids indicated that there were recognizable differences. However, size-free (sheared) discriminant analysis indicated that these differences were largely size-dependent, with much overlap of the four eastern and two hybrid populations but no overlap with I. pacificus from California. Analysis of chromosomes (morphology and C band) indicated no differences between the Georgia and Massachusetts populations but showed a difference between them and the California population of I. pacificus. Analysis of isozymes showed that the genetic identity value for the Georgia and Massachusetts populations was within the normal range for conspecific populations, whereas the California population indicated congeneric but not conspecific relatedness to the Georgia and Massachusetts populations. Life cycle data collected under similar laboratory conditions showed no differences in length of feeding and molting periods among Georgia, Massachusetts, and California populations. These data and results of the work of other authors on tick host preferences and vector competence indicate that I. dammini is not a valid species separate from I. scapularis. Because the name Ixodes scapularis Say, 1821, has priority over the name Ixodes dammini Spielman, Clifford, Piesman & Corwin, 1979, I. dammini is relegated to a junior subjective synonym of I. scapularis (based on Article 23 of the International Code of Zoological Nomenclature).

cis-bis(pyridine)platinum(II) organoamides with unexpected growth inhibition properties and antitumor activity

The platinum(II) organoamides [Pt(NRCH2)2L2] (L = pyridine (py), R = p-HC6F4, C6F5,p-IC6F4,p-CIC6F4,p-C6F5C6F4; L = 4-methylpyridine, R = p-HC6F4) and [Pt(NRCH2CH2NR')(py)2] (R = p-HC6F4, R' = C6F5, p-BrC6F4, or p-MeC6F4) inhibit the growth of murine L1210 leukemia cells in culture with ID50 values for continuous exposure in the range 0.6-2.7 microM. Representative complexes are also active against L1210 cells in 2-h pulse exposures, as well as against the cisplatin-resistant variant L1210/DDP and human colonic carcinoma cell lines HT 29 and BE. Three complexes [Pt(NRCH2)2L2] (R = p-HC6F4, C6F5, or p-IC6F4) have good activity (T/C greater than or equal to 180%) against P388 leukemia in mice, and all other compounds tested are active except when R = p-C6F5C6F4, L = py. Although the molecular basis of the biological activity of these complexes is not known, the observation of good activity for amineplatinum(II) compounds with no hydrogen substituents on the nitrogen donor atoms introduces a new factor in the anticancer behavior of platinum(II) complexes.

4-(6'-Methoxy-3',4'-dihydronaphthalen-1'-yl)butan-2-one and the Derived Guareschi Imide

4-(6′-Methoxy-3′,4′-dihydronaphthalen-1′-yl)butan-2-one (6b) was condensed with ethyl cyano-acetate to give a mixture of the geometric isomers of the α, β unsaturated cyano ester (8), reaction of which with the anion derived from cyanoacetamide gave the Guareschi imide (7). Attempts to hydrolyse this to 3-[2′-(6″-methoxy-3″,4″-dihydronaphthalen-1″-yl)ethyl]-3-methylglutaric acid (4) gave only polymeric material. The preparations of 2,2-ethylenedioxy-4-(6′-methoxynaphthalen-1′-yl)butane (5a) and the corresponding butanone (5b) are also described.

Preparation of 2-(3-Bromo-1-methylpropyl)-1,3-dioxolan and the Corresponding Chloride From 2-Methylbutyrolactone

Lithium aluminium hydride reduction of ethyl 4-chloro-2-methylbutanoate (4a), derived from 3-methyldihydrofuran-2(3H)-one (2-methylbutyrolactone) (1), gave 4-chloro-2-methylbutan-1-ol (5a), oxidation of which with pyridinium chlorochromate afforded 4-chloro-2-methylbutanal (8a). The aldehyde (8a) was converted into 2-(3?-chloro-1′-methylpropyl)-1,3-dioxolan (7a) in 47% overall yield from (1). 2-(3′-Bromo-1′-methyIpropyl)-1,3-dioxolan (7b) was similarly obtained in 49% overall yield from (1). Attempted conversion of 3-methyltetrahydrofuran-2-ol (2) into the corresponding cyclic ethylene acetal gave epimeric mixtures of 2-(3′-methyltetrahydrofuran-2′-yloxy)ethanol (6) and 2,2′-ethylenedioxybis(3-methyltetrahydrofuran) (9).

Synthesis of 2-(5',5'-Ethylenedioxy-1'-methylcyclopent-2'-en-1'-yl)ethanol, and Some 2H-Cyclopenta[b]furan Derivatives Formed by Intramolecular Displacement Reactions

Exchange dioxolanation of 2-methyl-2-(prop-2′-enyl)cyclopentane-1,3-done (1b) gave 3,3- ethylenedioxy-2-methyl-2-(prop-2′-enyl) cyclopentan-1-one (2) which, upon reduction and esterification , afforded the epimeric 3,3-ethylenedioxy-2-methyl-2-(prop-2′-enyl) cyclopent-1-yl benzoates (6d). Oxidative cleavage of the terminal double bond in (6d),followed by sodium borohydride reduction yielded 3,3-ethylenedioxy-2-(2'-hydroxyethyl)-2-methylcyclopent-1-yl benzoate (4b) which underwent acid- catalysed rearrangement to 6a-(2′-hydroxyethoxy)-3a- methylhexahydrocyclopenta [b]furan-4-yl benzoate (8b). Flash vacuum pyrolysis of the t- butyldimethylsilyl ether (12), derived from the hydroxy acetal (4b), afforded 3-[2′- (t- butyldimethylsilyloxy )ethyl]-4,4-ethy1enedioxy-3-methylcyclopent-1-ene (14) which upon selective cleavage of the silyl ether group gave 2-(5′,5′-ethylenedioxy-1′-methylcyclopent- 2'′en-1′-y1)ethanol (7). Reaction of the mesylate (16) of (7) with lithium bromide or iodide in tetrahydrofuran at 50-55� for several hours yielded some of the corresponding 3-(2′-haloethyl) compounds (17), but gave mainly the rearranged 6a-(2′-haloethoxy)-3a-methyl-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]furans (19a) and (19b). Some related chemistry is described.

Organization and evolution of repeated DNA sequences in closely related plant genomes

In common with many other eukaryotic species, the genomes of species in the genus Allium contain a high proportion of repeated DNA sequences, which may be implicated in the considerable differences in genome size that are seen between even very closely related species. The gross organization of repetitive sequences within the genome of Allium sativum and of some other related species has been investigated using DNA/DNA hybridization studies. Such studies show that there has been much modulation in the amounts of different repeated DNA families during the evolution of the genus Allium; these repetitive elements are interspersed in all species with sequences of low repetition. The organization and distribution of one particular repetitive family within the genus has been examined using a cloned hybridization probe. Hybridization of this probe to DNA from related genomes reveals that this element is present in all Allium species examined, but with large-scale modulation of its abundance, and some considerable changes in its sequence environment. The evolution of such genome-specific arrangements of common repetitive elements and the possible mechanisms by which they might be maintained are discussed.