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M Kreitman

Publications and source records attributed to M Kreitman.

48 records · Page 3Linked to original sources
PubMed1993

The lepidopteran mitochondrial control region: structure and evolution.

For several species of lepidoptera, most of the approximately 350-bp mitochondrial control-region sequences were determined. Six of these species are in one genus, Jalmenus; are closely related; and are believed to have undergone recent rapid speciation. Recent speciation was supported by the observation of low interspecific sequence divergence. Thus, no useful phylogeny could be constructed for the genus. Despite a surprising conservation of control-region length, there was little conservation of primary sequences either among the three lepidopteran genera or between lepidoptera and Drosophila. Analysis of secondary structure indicated only one possible feature in common--inferred stem loops with higher-than-random folding energies--although the positions of the structures in different species were unrelated to regions of primary sequence similarity. We suggest that the conserved, short length of control regions is related to the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In addition, determination of flanking sequences for one Jalmenus species indicated (i) only weak support for the available model of insect 12S rRNA structure and (ii) that tRNA translocation is a frequent event in the evolution of insect mitochondrial genomes.

Animals↗
PubMed1992

Molecular diagnosis of Borrelia burgdorferi infection (Lyme disease).

In spite of significant advances in immunologically based testing, accurate diagnosis of Lyme borreliosis remains problematic. To address this issue, a DNA amplification-based diagnostic test was developed utilizing the polymerase chain reaction (PCR) and oligonucleotide primers specific for the OspA and OspB genes of Borrelia burgdorferi. In this approach, a relatively large DNA fragment is amplified with an outer set of primers, and a "nested" internal sequence of the PCR product subsequently reamplified with an inner set of primers. This nested approach coupled with simple differential centrifugation allowed specific detection of as few as four B. burgdorferi organisms mixed in 2 ml of blood. This methodology was utilized on patients' samples, and it allowed detection of B. burgdorferi in the peripheral blood and urine of several individuals with clinical evidence of Lyme borreliosis. PCR became negative and symptoms improved following antibiotic therapy of treated individuals. These studies suggest that direct detection of Borrelia in infected individuals can aid in diagnosis and evaluation of therapy for Lyme borreliosis.

Base Sequence↗
PubMed1991

Adaptive protein evolution at the Adh locus in Drosophila.

Proteins often differ in amino-acid sequence across species. This difference has evolved by the accumulation of neutral mutations by random drift, the fixation of adaptive mutations by selection, or a mixture of the two. Here we propose a simple statistical test of the neutral protein evolution hypothesis based on a comparison of the number of amino-acid replacement substitutions to synonymous substitutions in the coding region of a locus. If the observed substitutions are neutral, the ratio of replacement to synonymous fixed differences between species should be the same as the ratio of replacement to synonymous polymorphisms within species. DNA sequence data on the Adh locus (encoding alcohol dehydrogenase, EC 1.1.1.1) in three species in the Drosophila melanogaster species subgroup do not fit this expectation; instead, there are more fixed replacement differences between species than expected. We suggest that these excess replacement substitutions result from adaptive fixation of selectively advantageous mutations.

Alcohol Dehydrogenase↗
PubMed1991

Inferring the evolutionary histories of the Adh and Adh-dup loci in Drosophila melanogaster from patterns of polymorphism and divergence.

The DNA sequences of 11 Drosophila melanogaster lines are compared across three contiguous regions, the Adh and Adh-dup loci and a noncoding 5' flanking region of Adh. Ninety-eight of approximately 4750 sites are segregating in the sample, 36 in the 5' flanking region, 38 in Adh and 24 in Adh-dup. Several methods are presented to test whether the patterns and levels of polymorphism are consistent with neutral molecular evolution. The analysis of within- and between-species polymorphism indicates that the region is evolving in a nonneutral and complex fashion. A graphical analysis of the data provides support for a hypothesized balanced polymorphism at or near position 1490, site of the amino acid replacement difference between Adhf and Adhs. The Adh-dup locus is less polymorphic than Adh and all 24 of its polymorphisms occur at low frequency--suggestive of a recent selective substitution in the Adh-dup region. Adhs alleles form two distinct evolutionary lineages that differ one from another at a total of nineteen sites in the Adh and Adh-dup loci. The polymorphisms are in complete linkage disequilibrium. A recombination experiment failed to find evidence for recombination suppression between the two allelic classes. Two hypotheses are presented to account for the widespread distribution of the two divergent lineages in natural populations. Natural selection appears to have played an important role in governing the overall patterns of nucleotide variation across the two-gene region.

Alcohol Dehydrogenase↗
PubMed1991

Lack of polymorphism on the Drosophila fourth chromosome resulting from selection.

Evolutionary processes can be inferred from comparisons of intraspecific polymorphism and interspecific divergence. We sequenced a 1.1-kb fragment of the cubitus interruptus Dominant (ciD) locus located on the nonrecombining fourth chromosome for ten natural lines of Drosophila melanogaster and nine of Drosophila simulans. We found no polymorphism within D. melanogaster and a single polymorphism within D. simulans; divergence between the species was about 5%. Comparison with the alcohol dehydrogenase gene and its two flanking regions in D. melanogaster, for which comparable data are available, revealed a statistically significant departure from neutrality in all three tests. This lack of polymorphism in the ciD locus may reflect recent positive selective sweeps on the fourth chromosome with extreme hitchhiking generated by the lack of recombination. By simulation, we estimate there to be a 50% chance that the selective sweeps occurred within the past 30,000 years in D. melanogaster and 75,000 in D. simulans.

Alcohol Dehydrogenase↗
PubMed1990

Cloning regions of the Drosophila genome by microdissection of polytene chromosome DNA and PCR with nonspecific primer.

A simple and rapid procedure to isolate clones carrying sequences from a specific region of the polytene chromosome of Drosophila is demonstrated. The procedure involves microdissection of the region of interest, amplification of the DNA by PCR using a primer designed to prime the synthesis nonspecifically, labeling of the amplified DNA using the random primer method, and screening of a standard library with the probe to identify and isolate clones carrying sequences homologous to the dissected region. This procedure has the potential to replace the difficult procedure of microcloning, as well as facilitate chromosome walking.

Animals↗
PubMed1987

A test of neutral molecular evolution based on nucleotide data.

The neutral theory of molecular evolution predicts that regions of the genome that evolve at high rates, as revealed by interspecific DNA sequence comparisons, will also exhibit high levels of polymorphism within species. We present here a conservative statistical test of this prediction based on a constant-rate neutral model. The test requires data from an interspecific comparison of at least two regions of the genome and data on levels of intraspecific polymorphism in the same regions from at least one species. The model is rejected for data from the region encompassing the Adh locus and the 5' flanking sequence of Drosophila melanogaster and Drosophila sechellia. The data depart from the model in a direction that is consistent with the presence of balanced polymorphism in the coding region.

Alcohol Dehydrogenase↗
PubMed1987

Sequence of the structural gene for xanthine dehydrogenase (rosy locus) in Drosophila melanogaster.

We determined the nucleotide sequence of a 4.6-kb EcoRI fragment containing 70% of the rosy locus. In combination with information on the 5' sequence, the gene has been sequenced in entirety. rosy cDNAs have been isolated and intron/exon boundaries have been determined. We find an open reading frame which spans four exons and would encode a protein of 1335 amino acids. The molecular weight of the encoded protein (xanthine dehydrogenase), based on the amino acid translation, is 146,898 daltons which agrees well with earlier biophysical estimates. Characteristics of the protein are discussed.

Amino Acid Sequence↗
PubMed1986

Genetic uniformity in two populations of Drosophila melanogaster as revealed by filter hybridization of four-nucleotide-recognizing restriction enzyme digests.

A filter hybridization method is described for identifying restriction-site and insertion/deletion variation by using restriction enzymes that recognize four-nucleotide sequences and denaturing polyacrylamide gels for separating fragments. Eighty-seven lines of Drosophila melanogaster representing two natural populations were surveyed over a 2.7-kilobase region encompassing the alcohol dehydrogenase locus. Fifty distinct haplotypes were identified from 17 restriction-site and 11 insertion/deletion polymorphisms and from one allozyme polymorphism. There was no evidence for genetic differentiation between an East-Coast and a West-Coast (North American) sample. This technique has widespread applications in screening for DNA polymorphism.

Alcohol Dehydrogenase↗
PubMed1980

Assessment of variability within electromorphs of alcohol dehydrogenase in Drosophila melanogaster.

Ninety-six isochromosomal lines of Drosophila melanogaster from a natural population were screened electrophoretically for unusual mobility variants at the alcohol dehydrogenase locus, using a total of eight conditions of acrylamide electrophoresis. No additional mobility variation was found among the 50 "slow" and 46 "fast" mobility lines beyond that detected by standard methods of electrophoresis. However, two thermostability variants recovered by R. MILKMAN from a natural population, whose electrophoretic mobilities were previously thought to be distinguishable from those of "standard" alleles, are distinguishable from the standard electromorphs by these procedures. These results suggest that the Adh locus, although polymorphic, does not harbor substantial amounts of "hidden" allelic variability. This study also reports the appearance of substantial mobility variation among isogenic lines that can be induced under specific conditions of sample preparation involving the pretreatment of samples with NAD and acetone. However, genetic analysis demonstrates that this variability cannot be attributed to allelic differences at the structural locus, but instead appears to be dependent upon the concentration of the enzyme in a sample. These results are discussed in relation to the distribution of allelic variation at other enzyme loci.

Alcohol Oxidoreductases↗
PubMedDate not supplied

Nucleotide polymorphism at the alcohol dehydrogenase locus of Drosophila melanogaster.

The sequencing of eleven cloned Drosophila melanogaster alcohol dehydrogenase (Adh) genes from five natural populations has revealed a large number of previously hidden polymorphisms. Only one of the 43 polymorphisms results in an amino acid change, the one responsible for the two electrophoretic variants (fast, Adh-f, and slow, Adh-s) found in nearly all natural populations. The implication is that most amino acid changes in Adh would be selectively deleterious.

Alcohol Dehydrogenase↗