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Biomedical subjects

D M Glover

Publications and source records attributed to D M Glover.

138 records · Page 8Linked to original sources
PubMed1980

A DNA segment from D. melanogaster which contains five tandemly repeating units homologous to the major rDNA insertion.

We describe a cloned segment of D. melanogaster DNA (cDm219) that contains five tandemly arranged sequence units homologous to the type I insertion sequence found in the majority of 28S rRNA genes on the X chromosome. Heteroduplex studies show that two of the units have a deletion corresponding to a 1.1 kb piece of DNA close to the right-hand end of the type I insertion. Another unit has a 7.5 kb sequence (zeta) substituted for a 0.95 kb piece of DNA close to the left-hand part of the type I rDNA insertion. The two remaining units are interrupted by the Col E1 plasmid vector. There are also differences in the restriction endonuclease cleavage maps both between the units of cDm219 themselves and compared to the restriction endonuclease cleavage maps of cloned rDNA segments that contain type I insertions. Quantitation of the gel transfer hybridization of zeta element probes to restriction endonuclease digests of D. melanogaster DNA indicates there are 30--40 copies of zeta sequences distributed in seven major arrangements within the haploid genome. The hybridization of zeta and insertion sequence probes to a library of D. melanogaster DNA segments cloned in bacteriophage lambda indicates at least 4--6 copies of the zeta element could be linked to insertion sequences. The common site of in situ hybridization of zeta sequences is to the chromocentral heterochromatin of polytene chromosomes.

Animals↗
PubMed1979

Differential replication of ribosomal gene repeats in polytene nuclei of Drosophila.

The genes coding for the 18S and 28S rRNAs in D. melanogaster were examined using Southern transfers of DNA from diploid or polytene tissue. A ribosomal gene repeat 12 kb in length is present in DNA from diploid tissue of males and is the major repeat on the Y chromosome. This repeat is present in low amounts on the X chromosome, which contains major repeats of 17 and 11.5 kb. In polytene nuclei of males, the 12 kb band is disproportionately replicated, and only a very low amount of the 11.5 kb repeat and no 17 kb repeat are detected. Polytene nuclei of females contain reduced amounts of the 17 kb repeat relative to the 11.5 kb repeat. This disproportionate replication of specific ribosomal gene repeats suggests that polytenization of the rDNA may involve an extrachromosomal mechanism. Evidence that genes from only one nucleolus organizer are replicated during polytenization in X/Y and X/X flies is discussed. A method for analyzing DNA from tissue of individual larvae was developed to test for population heterogeneity in ribosomal gene structure. Heterogeneity was observed in the ribosomal genes of three Ore R lines, four other D. melanogaster strains and between males and females of the same strain.

Animals↗
PubMed1977

A novel arrangement of the 18S and 28S sequences in a repeating unit of Drosophila melanogaster rDNA.

The sequences corresponding to the 18S and 28S rRNAs have been mapped within a cloned 17 kilobase (kb) fragment formed by Eco R1 cleavage of Drosophila melanogaster rDNA. This fragment, Dm103, represents the longer of two major types of repeating units that are present in the rDNA of this fly, and was cloned as a hybrid plasmid, pDm103, consisting of Dm103 inserted at the Eco R1 site of the pSC101 vector (Glover et al., 1975). Mapping of the 18S and 28S rDNA in Dm103 was accomplished by quantitative determination of the amount of these rDNAs in each member of an ordered set of restriction fragments obtained by Hind III and Eco R1 ccleavage of pDm103. The amounts of 18S and 28S rDNAs were determined by hybridization of the rRNAs to fragments that were purified by cloning, and an unambiguous order of the fragments within pDm103 was established by heteroduplex mapping and from the stoichiometry of the fragment lengths. The resulting map revealed that the 4 kb of 28S rDNA within the long repeating unit represented by Dm103 is divided into two blocks that are separated by 5.4 kb of DNA of unknown function. It is this unusual arrangement of the 28S rDNA that distinguishes the long repeating units (17 kb) from the short units (11.5) kb), whose 4 kb of 28S rDna is confined to a single block, as is shown in the accompanying paper (White and Hogness, 1977). The remainder of the DNA in this long unit appears to be typically arranged, with the 2 kb of 18S rDNA confined to a single block that is separated by about 1 kb from the closest block of 28S rDNA.

Animals↗
PubMed1977

Cloned segment of Drosophila melanogaster rDNA containing new types of sequence insertion.

A cloned 14.3-kbase segment of Drosophila melanogaster rDNA (Dm207) is described in which only a 4-kbase region is homologous to a cloned 17-kbase rDNA repeating unit, Dm103; this 4-kbase region consists of part of the 28S rRNA gene and most but not all of the adjacent transcribed spacer that normally connects the 18S and 28S genes. The transcribed spacer in Dm207 is interrupted by a 2.2-kbase stretch of DNA that does not contain any 18S gene sequences. At the other end of the 4-kbase homology, the 28S gene is interrupted by an 8.1-kbase stretch of DNA at a position equivalent to the site of the 28S insertion found in the 17-kbase units. The question of whether the 2.2-kbase and 8.1-kbase interrupter segments in Dm207 derive from longer insertions into the transcribed spacer and 28S genes of a very long repeating unit (greater than or equal to 22 kbases) or represent a region of the chromosomal DNA into which a 4-kbase fragment of rDNA has been inserted is discussed.

Base Sequence↗
PubMed1975

Characterization of six cloned DNAs from Drosophila melanogaster, including one that contains the genes for rRNA.

pDm plasmids were constructed from D. melanogaster and pSC101 DNAs by a modification of the EcoR1-ligase method which insured that each hybrid molecule contained a single segment of D. melanogaster chromosomal DNA (Dm segment). The sequences in the Dm segments of six cloned pDm DNAs were mapped within the D. melanogaster polytene chromosomes by in situ hybridization, and their repetition frequencies within the Dm segment and within the genome were determined. Four of these segments consist of sequences that are confined to single chromomeric regions in the polytene chromosomes and exhibit little or no repetition. The characteristics of this group, and also two of three Dm segments analyzed earlier (Wensink et al., 1974), are inconsistent with tandem repetition models of the chromomere. By contrast, the other two Dm segments contain moderately repetitive sequences that are located in the heterochromatin. One of these appears to be a segment of the Y chromosome in which about half the sequences are nonrepetitive and half are repeated about 33 times per genome, though they are not repeated within the segment. The second contains the DNA coding for 18 and 28S rRNA.

Animals↗