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M L Pardue

Publications and source records attributed to M L Pardue.

At least 55 records · Page 3Linked to original sources
PubMed1989

Sequence evolution of the Drosophila heat shock locus hsr omega. I. The nonrepeated portion of the gene.

The locus which we now call hsr omega was originally identified as a large heat shock puff in polytene region 93D of Drosophila melanogaster. This puff was subsequently found to have several phenotypic characteristics that distinguished it from other heat shock puffs. These characteristics include induction by a number of agents that do not induce other puffs and the presence of large ribonucleotide particles that are not found elsewhere. Each Drosophila species has one heat shock puff with these phenotypes. In contrast to the strong sequence conservation seen in puffs coding for heat shock proteins, very little cross-hybridization is detected between hsr omega loci in different species, suggesting that the hsr omega loci are diverging rapidly. Comparative analyses of the hsr omega locus from D. melanogaster, D. pseudoobscura, and D. hydei show that, despite the sequence change, the structure of the locus and its transcripts has been conserved, along with a number of short regions of the sequence. The short regions of conservation offer some clues to the function of this unusual locus. In addition, these comparisons offer a view of the evolution of a gene whose primary function does not appear to be protein coding.

Animals↗
PubMed1989

Nonrandom distribution of long mono- and dinucleotide repeats in Drosophila chromosomes: correlations with dosage compensation, heterochromatin, and recombination.

Long stretches of (dC-dA)n.(dT-dG)n, abbreviated CA/TG, have a distinctive distribution on Drosophila chromosomes (M.L. Pardue, K. Lowenhaupt, A. Rich, and A. Nordheim, EMBO J. 6:1781-1789, 1987). The distribution of CA/TG suggests a correlation with the overall transcriptional activity of chromosomal regions and with the ability to undergo meiotic recombination. These correlations are conserved among Drosophila species and may indicate one or more chromosomal functions. To test the generality of these findings, we analyzed the distribution of the rest of the six possible mono- and dinucleotide repeats (A/T, C/G, AT/AT, CA/TG, CT/AG, and CG/CG). All but CG/CG were present at significant levels in the genomes of the six Drosophila species studied; however, A/T levels were an order of magnitude lower than those of the other sequences. Data base analyses suggested that the same sequences are present in other eucaryotes. Like CA/TG, both CT/AG and C/G showed increased levels on dosage-compensating chromosomes; however, the individual sites clearly differed for each sequence. In contrast, A/T and AT/AT, although present in Drosophila DNA, could not be detected in situ in polytene chromosomes. We also used in situ hybridization to analyze the neo-Y chromosome of Drosophila miranda, an ancestral autosome that has become attached to the Y chromosome and is now partially heterochromatic. The neo-Y has acquired repeated DNA sequences; we found that the added sequences are as devoid of mono- and dinucleotide repeats as other heterochromatin. The distribution and function of these sequences are likely to result from both their repetitious nature and base contents.

Animals↗
PubMed1988

A spontaneously opened ring chromosome of Drosophila melanogaster has acquired He-T DNA sequences at both new telomeres.

Ring chromosomes that have been opened to give linear chromosomes offer an opportunity to study the DNA sequences associated with new chromosome ends. The Drosophila melanogaster chromosome C(1)A was originally a ring chromosome, consisting of two linked X chromosomes, and thus had no telomeres. This chromosome has spontaneously opened in polytene region 13, a region near the middle of the euchromatic arm of the X chromosome. The opening of the ring has produced two new telomeres on the C(1)A chromosome. Each of the new telomeres has acquired He-T DNA sequences. He-T DNA is a complex family of repeated sequences found in the telomeric and pericentric heterochromatin of D. melanogaster chromosomes. He-T DNA sequences are detected, at various levels, in the most distal band on the end of each polytene chromosome in all D. melanogaster stocks. To our knowledge, these sequences have never been detected within the euchromatic chromosomal regions in any stock. The strong correlation between He-T DNA sequences and telomeric regions suggests that He-T sequences may have a role in organizing or maintaining the ends of chromosomes. The association of He-T DNA with newly acquired telomeres in a formerly euchromatic region, polytene region 13, strengthens this correlation.

Animals↗
PubMed1988

Studies of the genetic organization of the vestigial microregion of Drosophila melanogaster.

The region of the second chromosome of Drosophila melanogaster defined by Df(2R)vgB was screened for recessive lethal and visible mutations. Fifty-eight new recessive alleles fall into 17 complementation groups. Many new vg alleles were also isolated in a screen for new vg deficiencies. The breakpoints of the new vg deficiencies were nonrandomly distributed. The distal breakpoints of twelve of 20 deficiencies overlapping Df(2R)vgB are genetically identical to that of Df(2R)vgD, coinciding with the position of a complex, pleiotropic locus, l(2)49Ea-Psc-Su(z)2.

Alleles↗
PubMed1987

(dC-dA)n.(dG-dT)n sequences have evolutionarily conserved chromosomal locations in Drosophila with implications for roles in chromosome structure and function.

In situ hybridization of (dC-dA)n.(dG-dT)n to the polytene chromosomes of Drosophila melanogaster reveals a clearly non-random distribution of chromosomal sites for this sequence. Sites are distributed over most euchromatic regions but the density of sites along the X chromosome is significantly higher than the density over the autosomes. All autosomes show approximately equal levels of hybridization except chromosome 4 which has no detectable stretches of (dC-dA)n.(dG-dT)n. Another striking feature is the lack of hybridization of the beta-heterochromatin of the chromocenter. The specific sites are conserved between different strains of D. melanogaster. The same overall chromosomal pattern of hybridization is seen for the other Drosophila species studied, including D. simulans, a sibling species with a much lower content of middle repetitive DNA, and D. virilis, a distantly related species. The evolutionary conservation of the distribution of (dC-dA)n.(dG-dT)n suggests that these sequences are of functional importance. The distribution patterns seen for D. pseudoobscura and D. miranda raise interesting speculations about function. In these species a chromosome equivalent to an autosomal arm of D. melanogaster has been translocated onto the X chromosome and acquired dosage compensation. In each species the new arm of the X also has a higher density of (dC-dA)n.(dG-dT)n similar to that seen on other X chromosomes. In addition to correlations with dosage compensation, the depletion of (dC-dA)n.(dG-dT)n in beta-heterochromatin and chromosome 4 may also be related to the fact that these regions do not normally undergo meiotic recombination.

Animals↗
PubMed1987

Isolation and characterization of the gene for myosin light chain two of Drosophila melanogaster.

A recombinant lambda-phage DNA clone containing Drosophila melanogaster sequences encoding the gene for myosin light chain (MLC) two has been isolated from a library of randomly sheared DNA. The Drosophila MLC2 gene is located in region 99E1-3 on the right arm of chromosome 3, several bands removed from the site reported for the other myosin light chain gene at 98B. The MLC2 sequence at 99E1-3 appears to encode all of the isoforms of Drosophila MLC2. The polypeptide encoded at 99E was identified as MLC2 by the following criteria: the in vitro translation product is identical in size to MLC2 isolated from Drosophila muscle, and on two-dimensional gels the in vitro translation product can be separated into two or more peptides that co-migrate with isoforms of larval and thoracic MLC2. RNA encoding the polypeptide was detected in embryos only after the onset of muscle differentiation and was also abundant in adult thoracic muscle. The nucleotide sequence of cDNA generated from late embryonic RNA would be translated to yield a protein sequence with multiple regions of homology to vertebrate MLC2. (There are shorter regions of homology to vertebrate MLC1). Like a number of vertebrate muscle proteins, Drosophila MLC2 has an acetylated amino-terminus.

Acetylation↗
PubMed1986

A Drosophila heat shock locus with a rapidly diverging sequence but a conserved structure.

Cytological studies have shown that the heat shock loci 93D of Drosophila melanogaster and 2-48B of Drosophila hydei have several characteristics which suggest that they are homologous loci, yet sequence homology is barely detectable by cross-hybridization. Using cloned DNA sequences we have compared the two loci. Both loci produce transcripts of similar size and number. We have characterized the three predominant transcripts. In each species all three transcripts start at or about the same place within the unique portion of the gene. The longest transcript (approximately 9-10 kilobases) continues through several kilobases of short tandem repeats. The two shorter (1.9 and 1.2 kilobases) transcripts terminate 5' to the repeats. The repeat sequences are strongly conserved within a species but between species they have diverged both in length and in sequence. The longest homology is 9 nucleotides. The unique portions have also diverged significantly but do have some regions of conserved sequence. In both species the cytoplasmic transcript is spliced and polyadenylated but does not appear to contain a significant open reading frame. Thus, although the sequence of this locus has diverged significantly there are conserved features which suggest that the function of the locus is also conserved.

Animals↗
PubMed1986

Analysis of Z-DNA in fixed polytene chromosomes with monoclonal antibodies that show base sequence-dependent selectivity in reactions with supercoiled plasmids and polynucleotides.

Five monoclonal anti-Z-DNA antibodies were characterized with respect to their binding of synthetic nucleic acid polymers and of supercoiled circular plasmid DNA. All of the antibodies reacted only with DNA in the Z-conformation; however, they fell into two classes on the basis of sequence specificity. One class, with broad specificity, reacted well with all sequences in the Z-form, including poly(dG-dC), poly(dG-dm5C), and poly (dG-dBr5C) in linear polymers and poly(dG-dC)n and poly[(dC-dA)n.(dT-dG)n] sequences in supercoiled plasmids. The other class bound only Z-DNA formed by poly(dG-dC). Binding of the monoclonal antibodies specifically to inserts of Z-DNA-forming sequences in plasmids was mapped directly by cross-linking of antibody to the DNA, digestion with restriction nuclease, and electrophoretic analysis of both the unbound fragments and the bound fragments recovered from immune complexes. The monoclonal antibodies were used for indirect immunofluorescence staining of Drosophila polytene chromosomes fixed by two procedures. One procedure yielded chromosomes with Z-specific antibody binding in many interbands, a few specific bands, and parts of some puffs. On chromosomes fixed by the second procedure, antibody staining appeared to follow the DNA concentration, staining all bands brightly. For each fixation procedure, chromosomes showed the same staining pattern with each of the broad specificity monoclonal antibodies that had been seen with polyclonal antibodies. The antibodies that reacted only with poly(dG-dC) and poly (dG-dC)n plasmid inserts did not stain chromosomes fixed by either protocol. We conclude that stretches of poly(dG-dC)n sequences do not contribute significantly to the presence of Z-DNA in fixed polytene chromosomes of Drosophila melanogaster.

Animals↗
PubMed1986

Heat shock locus 93D of Drosophila melanogaster: a spliced RNA most strongly conserved in the intron sequence.

The Drosophila melanogaster heat shock locus at 93D encodes at least three overlapping transcripts, 10-12 kilobases (kb), 1.9 kb, and 1.2 kb. The abundance of the three transcripts is significantly increased during heat shock; however, all are also found in non-heat-shocked cells. The 1.2-kb transcript is found in the cytoplasm. Sequence analysis of a 1.1-kb cDNA clone representing sequences within the 1.2-kb transcript and comparison to genomic sequences indicate that it is spliced; 700 base pairs of sequence found in genomic DNA are removed from the middle of the transcript. Sequence analysis further suggests that this RNA does not encode a heat shock protein. The largest open reading frame beginning with a methionine codon would encode a polypeptide of 34 amino acids. We have not been able to detect a heat shock-induced polypeptide of this size. A DNA clone from the analogous heat shock puff of Drosophila hydei has been analyzed by hybridization with the small subclones used to sequence the D. melanogaster cDNA plus a genomic fragment containing the 700-base-pair intron. Results of this hybridization indicated strong homology of the intron fragment. Weaker homology was detected with the two small fragments flanking the intron. Other fragments of the D. melanogaster cDNA showed no hybridization to the cloned D. hydei puff DNA.

Animals↗
PubMed1984

DNA-protein interactions in the Drosophila virilis mitochondrial chromosome.

The location of proteins on the mitochondrial DNA (mtDNA) of Drosophila virilis was investigated by Me3 psoralen photoreaction of mitochondria isolated from embryos. After photoreaction the mtDNA was purified and the pattern of DNA cross-linking was determined by electron microscopy of the DNA under totally denaturing conditions. The transcribed regions of the mtDNA molecule contained some uncross-linked regions, but such regions were infrequent and randomly distributed. In contrast, the A + T-rich region around the origin of replication of the mtDNA was usually protected from psoralen cross-linking. The data were best fit by two protected sites, each approximately 400 base pairs, compared to the four 400 base pair sites observed in the equivalent region of D. melanogaster mtDNA [Potter et al. (1980) Proc. Nat. Acad. Sci. USA 77, 4118-4122]. Thus this region of the mtDNA appears to be involved in a DNA-protein structure that is highly conserved even though the DNA sequence has diverged rapidly relative to protein-coding sequences.

Animals↗
PubMed1984

Chromosomal location of a major tRNA gene cluster of Xenopus laevis.

In Xenopus laevis, genes encoding tRNAPhe, tRNATyr, tRNAMet1, tRNAAsn, tRNAAla, tRNALeu, and tRNALys are clustered within a 3.18-kb (kilobase) fragment of DNA. This fragment is tandemly repeated some 150 times in the haploid genome and its components are found outside the repeat only to a limited extent. The fragment hybridizes in situ to a single site very near the telomere on the long arm of one of the acrocentric chromosomes of the group comprising chromosomes 13-18. All the chromosomes of this group also hybridize with DNA coding for oocyte-specific 5S RNA. The tRNA gene cluster is slightly proximal to the cluster of 5S RNA genes.

Animals↗
PubMed1984

Transfer of yeast telomeres to linear plasmids by recombination.

We have characterized two types of recombination events between linear plasmids and yeast chromosomal telomere-adjacent sequences (Y' elements). In one type of event, a linear plasmid restriction-cut within a Y' element regains the missing Y' DNA, and may also acquire additional Y' elements. This process is similar to the healing of broken chromosomes by recombination. In a second type of event, terminally added C1-3A sequences on the linear plasmid interact with C1-3A sequences located just internal to the chromosomal Y' elements, resulting in the addition of one to four Y' elements to the plasmid. Similar recombination events occurring between different chromosome ends could lead to the dispersal and amplification of telomere-adjacent sequences.

Base Sequence↗
PubMed1983

Telomere regions in Drosophila share complex DNA sequences with pericentric heterochromatin.

A 12 kb fragment of Drosophila melanogaster DNA cloned in a lambda phage, lambda T-A, is shown by in situ hybridization to contain sequences homologous to DNA at the extreme ends of each of the polytene chromosomes and to the pericentric sequences present in the beta heterochromatin. This pattern of hybridization is seen for each of the four D. melanogaster stocks that have been studied. Most of the sequence in lambda T-A shows no detectable homology to DNA within the banded chromosome arms. (The only exception is what appears to be a short mobile element inserted in lambda T-A. This portion of lambda T-A hybridizes with internal arm sites that vary from stock to stock). Analysis of restriction fragments of genomic DNA indicates that the sequences in lambda T-A are homologous to complex sets of repeated sequences that differ from stock to stock in D. melanogaster. Some, but not all, of the members of these sets are underreplicated during polytenization in D. melanogaster. The sequences in lambda T-A are also homologous to complex sets of repeated sequences in the genomes of other Drosophila species belonging to the melanogaster species group. Pericentric and telomeric localization is conserved in these related species, although analysis of DNA fragments shows marked changes in sequence organization on a finer scale. The constancy of the localization of lambda T-A-homologous sequences to telomeric and pericentric regions suggests that these sequences serve a function in those regions.

Animals↗
PubMed1983

The control of protein synthesis during heat shock in Drosophila cells involves altered polypeptide elongation rates.

When Drosophila tissue culture cells are shifted from 25 to 36 degrees C (heat shocked) the pre-existing mRNAs (25 degrees C mRNAs) remain in the cytoplasm but their translation products are underrepresented relative to the induced heat shock proteins. Many of these undertranslated 25 degrees C mRNAs are found in association with polysomes of similar size in heat-shocked and control cells. Furthermore, the messages encoding alpha-tubulin, beta-tubulin, and actin are found associated with one-third to one-half as many total ribosomes in heat-shocked cells as in cells incubated at 25 degrees C. Increased temperature should lead to increased output of protein per ribosome. However, the 25 degrees C proteins are actually synthesized at less than 10% of 25 degrees C levels in heat-shocked cells. Thus, the rates of both elongation and initiation of translation are significantly (15- to 30-fold) slower on 25 degrees C mRNAs than they are on heat shock mRNAs in heat-shocked cells.

Actins↗
PubMed1983

Z-DNA and the polytene chromosome.

Indirect immunofluorescence shows that antibodies specific for the Z conformation of DNA bind to D. melanogaster polytene chromosomes in a specific and reproducible pattern. In our acetic-acid-fixed preparations, the binding is predominantly to interband regions, to puffs, and to some specific bands. As might be expected, the pattern of binding can be affected by cytological procedures. Bands and interbands show significant differences in their susceptibility to these procedures. Although further study is needed, our studies give no evidence that acetic acid treatment of intact cells is capable of causing conversion of B-form and Z-form DNAs. Instead, the experiments suggest that the Z conformation is preferentially available in interbands and a few other chromosome regions.

Animals↗