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Biomedical subjects

M Meselson

Publications and source records attributed to M Meselson.

At least 37 records · Page 2Linked to original sources
PubMed1983

Accumulation of a specific subset of D. melanogaster heat shock mRNAs in normal development without heat shock.

During normal development in D. melanogaster, messenger RNAs for three of the seven heat shock proteins (hsp83, hsp28 and hsp26) accumulate in adult ovaries and are abundant in embryos until blastoderm. The three mRNAs appear to originate in nurse cells and subsequently pass, during stages 10-11, into the oocyte. Little if any of the four other heat shock mRNAs is present in unshocked ovaries or embryos at any time examined. Pre-blastoderm embryos fail to accumulate these heat shock mRNAs even if subjected to heat shock. The accumulation in normal oogenesis of mRNAs for only three of the seven heat shock proteins indicates the existence of differential, possibly multiple controls of heat shock gene expression, and suggests that heat shock proteins hsp83, hsp28 and hsp26 function in the oocyte or early embryo.

Animals↗
PubMed1983

Drosophila melanogaster mutations suppressible by the suppressor of Hairy-wing are insertions of a 7.3-kilobase mobile element.

Certain spontaneous mutations of Drosophila melanogaster are suppressed by su(Hw), the suppressor of Hairy-wing (3R-54.8). We find that mutations suppressible by su(Hw) result from insertions of a mobile element at the affected loci. The element, named gypsy, is approximately 7.3 kilobases long and includes 0.5-kilobase direct terminal repeats. It was first identified in DNA cloned from the bithorax chromosomal region of several Drosophila stocks carrying suppressible mutations of the bithorax complex. Cloned gypsy DNA was used as a probe to test for the association of gypsy with suppressible mutations at various other loci by hybridization in situ. Gypsy was found to be associated with 19 suppressible alleles at 10 different loci: yellow, Hairy-wing, scute, diminutive, cut, lozenge, forked, Beadex, hairy, and the bithorax complex. It was found with wild-type or nonsuppressible mutations at any of these loci. Gypsy DNA was also used as a probe to clone the element and adjacent unique DNA from the loci of some suppressible mutations. This confirmed the presence of the full-length element and also provided cloned DNA from the previously uncloned loci scute and cut. The suppressor of Hairy-wing is generally recessive and behaves as a null mutation. Thus, the disruption of normal gene function caused by the inserted gypsy element appears to require some product of the wild-type suppressor gene, su(Hw)+.

Animals↗
PubMed1983

Effects of high levels of DNA adenine methylation on methyl-directed mismatch repair in Escherichia coli.

Two methods were used in an attempt to increase the efficiency and strand selectivity of methyl-directed mismatch repair of bacteriophage lambda heteroduplexes in E. coli. Previous studies of such repair used lambda DNA that was only partially methylated as the source of methylated chains. Also, transfection was carried out in methylating strains. Either of these factors might have been responsible for the incompleteness of the strand selectivity observed previously. In the first approach to increasing strand selectivity, heteroduplexes were transfected into a host deficient in methylation, but no changes in repair frequencies were observed. In the second approach, heteroduplexes were prepared using DNA that had been highly methylated in vitro with purified DNA adenine methylase as the source of methylated chains. In heteroduplexes having a repairable cI/+ mismatch, strand selectivity was indeed enhanced. In heteroduplexes with one chain highly methylated and the complementary chain unmethylated, the frequency of repair on the unmethylated chain increased to nearly 100%. Heteroduplexes with both chains highly methylated were not repaired at a detectable frequency. Thus, chains highly methylated by DNA adenine methylase were refractory to mismatch repair by this system, regardless of the methylation of the complementary chain. These results support the hypothesis that methyl-directed mismatch repair acts to correct errors of replication, thus lowering the mutation rate.

Adenine↗
PubMed1981

Integration, transcription, and control of a Drosophila heat shock gene in mouse cells.

Mouse L cells were transformed with a cloned 3.6-kilobase (kb) segment of Drosophila melanogaster DNA carrying the 2.25-kb transcribed sequence for the Drosophila 70,000-dalton heat shock protein (hsp70) and 1.1 kb and 0.2 kb of 5' and 3' flanking DNA, respectively. Heat shock of one of three such transformed cell lines containing multiple copies of the intact Drosophila segment induced the abundant accumulation of transcripts of the Drosophila gene, with correct or nearly correct 5' and 3' termini. This provides evidence, in accord with earlier indications, that diverse eukaryotes, including vertebrates, have heat shock systems similar to that studied extensively in Drosophila. Our results suggest that the signals for heat shock transcription and the chromosomal sites with which they interact have been highly conserved in evolution and that the regulatory sequences controlling transcription of the gene for hsp70 lie within the 3.6-kb Drosophila segment.

Animals↗
PubMed1981

Sequence homologies in the 5' regions of four Drosophila heat-shock genes.

We report nucleotide sequences of the regions surrounding the 5' ends of the genes for Drosophila melanogaster heat-shock proteins hsp83, hsp68, and hsp26, located at chromosome positions 63BC, 95D, and 67B, respectively. As in other eukaryotic genes, the sequence T-A-T-A-A-A-A-T occurs about 30 nucleotides upstream from the sites of mRNA initiation. Three additional sequence homologies and a dyad symmetry were noted at approximately corresponding locations in the three genes and in the gene for another heat-shock protein, hsp70. We also found an intron near the 5' end of the hsp83 gene, with sequences at its boundaries typical of splice sites found in other organisms.

Animals↗
PubMed1980

Plasmid screening at high colony density.

A procedure is described for screening bacterial colonies containing recombinant plasmids by nucleic acid hybridization at high density, i.e., at 100 000 colonies per 150 mm diameter plate. Small colonies are established on nitrocellulose filters from which they can be faithfully replicated to additional filters. Chloramphenicol amplification may be carried out in situ before screening. The filters may be kept frozen for long-term storage of colonies which may be further replicated after thawing.

Cloning, Molecular↗
PubMed1980

Four heat shock proteins of Drosophila melanogaster coded within a 12-kilobase region in chromosome subdivision 67B.

Unique coding sequences for four heat shock proteins of Drosophila melanogaster, hsp 28, hsp 26, hsp 23, and hsp 22, are clustered in a 12-kilobase interval at chromosome subdivision 67B. The four genes are not transcribed in the same direction and each gives rise to a separate messenger RNA, with no indication of intervening sequences. Including the present results, the genes for all seven major heat shock proteins of D. melanogaster are now cloned are found to exhibit a variety of patterns of organization at the five loci they occupy.

Animals↗
PubMed1979

Studies of cloned sequences from four Drosophila heat shock loci.

DNA cloned from the D. melanogaster (Oregon R) heat shock loci at 63BC and 95D codes for the 83,000 and the 68,000 dalton heat shock proteins, respectively. Both coding sequences occur once per haploid genome. Sequences complementary to messenger RNA for the 70,000 dalton heat shock protein are represented five times, twice at 87A and three times at 87 C. The copies at 87A differ characteristically from those at 87C in an interval of a few hundred bp near the 5' end of the messenger sequence, and the corresponding two classes of hsp 70 messenger RNA are found on polysomes after heat shock. Within this differential region, there is about 15% divergence between messenger sequences cloned from the two loci, while in the rest of the messenger region examined the homology is much closer although still imperfect. Unexpectedly, considerable homology is found between the sequence for the 68,000 dalton heat shock protein at 95D and the sequences for the 70,000 dalton protein at 87A and 87C, and between these sequences and a site in 87D. Messenger RNA molecules of 2.4, 2.55 and 3.05 kb code for the 68,000, 70,000 and 83,000 dalton heat shock proteins and hybridize to apparently uninterrupted DNA sequences of 2.1, 2.25 and 2.6 kb, respectively.

Animals↗
PubMed1978

Sequence organization and transcription at two heat shock loci in Drosophila.

The heat shock loci of Drosophila melanogaster chromosome subdivisions 87A and 87C have been studied by using cloned DNA. Both sites contain a number of copies of a 2,4-kilobase (kb) region homologous to mRNA for the 70,000-dalton heat shock protein. In situ hybridization to chromosomal RNA shows that transcripts of this sequence accumulate at both sites after temperature elevation. At 87C there is a 1.5-kb repeated sequence homologous to another heat shock RNA. One cloned segment includes two to three tandem copies of this sequence located 0.8 kb from the beginning of a 2.4-kb message region. RNA complementary to the 1.5-kb repeat acccumulates at 87C after temperature elevation, but does not code for any known heat shock protein. In the sibling species D. simulans, there are sequences located and transcribed at 87A and 87C that are homologous to the melanogaster 2.4-kb message sequence. The 1.5-kb repeat, however, is absent from 87C in simulans and no heat shock RNA homologous to it can be detected.

Animals↗
PubMed1977

Transcription at two heat shock loci in Drosophila.

Transcription at two heat shock loci in Drosophila melanogaster, in subdivisions 87A and 57C, was investigated by hybridization in situ with 3H-labeled messenger, nuclear RNA and whole cell RNA from cells cultured at elevated temperature. What appears to be the same 9 x 10(5) dalton heat shock message hybridizes at both sites. At 87a, little additional hybridization is obtained with nuclear or whole cell RNA. In contrast, at 87C the saturation level of hybridization by nuclear and whole cell RNA is much higher than that obtained with the message alone. This evidence for extensive hybridization at 87C but not at 87A by RNA distinct from the message is confirmed by the finding that excess nonradioactive message competes away most of the hybridization by 3H-labeled nuclear and whole cell RNA at the latter locus but not at the former. The noncompetable RNA migrates on an electrophoretic gel as a heterogeneous population of molecules, extending to sizes both larger and smaller than the message. These and other observations lead to the conclusion that a 87A transcription includes little more than sequences complementary to the 9 x 10(5) dalton message, while at 87C, there are sequences complementary to the same message and extensive additional sequences complementary to other species of RNA.

Base Sequence↗
PubMed1976

Repair tracts in mismatched DNA heteroduplexes.

Heteroduplexes with mismatches at four sites were constructed from separated strands of lambda DNA and used to transfect Escherichia coli under recombinationless conditions. The output phages from 967 single cells in one experiment and 1016 in another were analyzed to determine the pattern of mismatch repair. A wide range of repair frequencies was found among the mismatches studied. Repair involving two or more close sites in the same heteroduplex occurs much more often on thesamestrandthanonopposite strands. Analysis of the pattern of repair suggeststhat repair tracts initiate at mismatches, propagate preferentially in the 5'leads to 3' direction, and extend an average distance of ca 3000 nucleotides.

Base Sequence↗
PubMed1976

Single burst study of rec- and red-mediated recombination in bacteriophage lambda.

Single bursts from three-point crosses of bacteriophage lambda were analyzed for recombination of markers several thousand nucleotide pairs apart. Single recombination, mediated by the rec system of Escherichia coli, is usually reciprocal. Double recombinants are also significantly correlated in single bursts, although the correlation is weaker than for reciprocal singles. Reciprocity is not found in crosses mediated by the lambda red system. With respect to certain other paraments of recombination, the two systems appear to be alike. Double recombinants usually result from one event, not from two independent single recombinations, and their average clone size is about half that of single recombinants. The results are discussed in terms of current molecular models of recombination.

Base Sequence↗
PubMed1975

Localization of RNA from heat-induced polysomes at puff sites in Drosophila melanogaster.

Heat treatment of D. melanogaster tissue culture cells causes drastic changes in the pattern of protein synthesis and the size distribution of polysomes. Like the heat shock puffs on polytene chromosomes which appear while preexisting puffs regress, heat shock proteins appear on gels while the synthesis of preexisting proteins is sharply reduced, and heat-induced polysomes appear on gradients after preexisting polysomes have disappeared. Most of the poly(adenylic acid)-containing RNA isolated from high-temperature polysomes sediments in sucrose gradients and migrates in gels as a rather narrow band. This RNA is of sufficient size to code for one particular protein that is found to account for more than half of the total synthesis at high temperature. The RNA hybridizes in situ mainly at chromosome sub-division 87B, the site of the major heat shock puff.

Adenine Nucleotides↗
PubMed1975

Mismatch repair in heteroduplex DNA.

DNA with base pair mismatches was prepared by annealing mixtures of genetically marked DNA from bacteriophage lambda. This heteroduplex DNA was used to transfect bacteria under conditions minimizing recombination. Genetic analysis of the progeny phages indicates that: (i) Mismatch repair occurs, usually giving rise to a DNA molecule with one chain with the genotype arising from repair and one parental chain. (ii) The frequency of repair of a given mismatch to wild type depends on the marker, ranging from 3 to 20%. (iii) Excision tracts may extend several hundred nucleotides but are usually shorter than about 2000 nucleotides. (iv) In Rec-mediated bacteriophage crosses, recombination of markers closer than about 10-3 nucleotide pairs frequently occurs by mismatch repair within heteroduplex DNA. (V) The average amount of heteroduplex DNA formed in a Rec-mediated recombination event is a few thousand nucleotide pairs.

Coliphages↗