The location of 5S (ribosomal) RNA genes in Drosophila hydei

The location of the 5S ribosomal RNA cistrons in band 2-23B1,2 of the polytene (salivary gland) chromosomes of Drosophila hydei was indicated by in situ hybridization of tritiated low molecular weight RNA fractionated from total in vivo synthesized larval RNA or from in vitro synthesized salivary gland RNA and competition of the hybridization of this RNA by 5S RNA obtained from calf lens ribosomes. -- At the submicroscopic level, band 2-23B1,2 in salivary gland chromosomes shows a compact organization. The adjacent region, 23B2, is slightly puffed and displays typical RNP particles, some of which may be observed close to band 2-23B1,2.     

Proportional polyploidization of 5S RNA genes in the ovary of Drosophila melanogaster mutants containing three 5S RNA gene loci

The 5S RNA gene content of polyploid cells of the ovary of Drosophila melanogaster has been compared in animals with two or three gene clusters. The amount of 5S RNA genes is exactly proportional to the number of gene clusters as determined by DNA-RNA filter hybridization. In contrast, the number of rDNA genes in endomitotic cells remains constant regardless of different numbers of nucleolus organizer regions (Spear, 1974).     

RNA metabolism during metamorphosis of Drosophila hydei

Determinations of total protein and RNA at various times after the beginning of the pharate pupal stage of Drosophila hydei, revealed an increase in both substances during the first 25 hr and a sudden decrease thereafter until 52 hr. From this time on the total amount of both protein and RNA increases slightly until emergence of the flies at 160 hr after the beginning of the pharate pupal stage. A similar pattern of changes was recorded for the total radioactivity as well as the specific activity of RNA labelled with ³H-uridine after the injection of the isotope immediately before the beginning of the pharate pupal stage.The migration profile of RNA labelled with ³H-uridine during larval development, revealed that shortly after the onset of the pharate pupal stage an essentially normal larval pattern consisting of major fractions of 28, 18, 8 to 9, and 4 to 7 S RNA. At 52 hr only the low molecular weight RNA was present. The ‘normal’ pattern was restored at the time of emergence of the flies, indicating re-utilization of degradation products of previously labelled RNA.     

Ecdysone-binding proteins in haemolymph and tissues of Drosophila hydei larvae

An α-ecdysone-binding protein fraction, approx. mol. wt. 120,000, has been demonstrated in haemolymph of Drosophila hydei late third instar larvae. The protein has been partly characterized by Sephadex G-25 filtration, hydroxylapatite chromatography, density gradient centrifugation, and ezyme digestion experiments. The protein-steroid complex appears to be heat stable. Binding of labelled ecdysone to the protein fraction is significantly reduced in competition experiments using unlabelled ecdysones.An ecdysone-binding protein fraction has been detected in hand-isolated total alimentary tract tissues (predominantly midgut, Malpighian tubules, and salivary glands) and in mass-isolated midgut and Malpighian tubules. The sedimentation properties of this protein-hormone complex are similar to those of the complex found in haemolymph.     

Evolution of 5S ribosomal RNA genes in the chromosomes of the virilis group of Drosophila

Drosophila melanogaster 5S ribosomal RNA labeled with ¹²⁵I was used as an in situ hybridization probe to localize complementary sequences in chromosomes of species in the Drosophila virilis group. Whereas virilis, the ancestral species, has two different 5S gene loci, the derived species show only one of these loci; in the two lines that have evolved from virilis it is the opposite locus that is conserved. The possible events leading to such an arrangement are discussed.The author was a Predoctoral Fellow supported by Grant GM 1974 from the National Institute of General Medical Sciences, National Institutes of Health.Contribution from Oak Ridge National Laboratory, operated by the Union Carbide Corporation for the U.S. Energy Research and Development Administration.     

Ectopic pairing and evolution of 5S ribosomal RNA genes in the chromosomes of Drosophila funebris

5S ribosomal RNA from Drosophila melanogaster labeled with ¹²⁵I was used to locate the 5S rRNA genes in chromosomes of D. funebris by means of in situ hybridization. Silver grains were observed at three distinct sites, one of which was a recognized reverse repeat. Only one half of the reverse repeat, however, hybridizes with 5S rRNA and the significance of this phenomenon is discussed. A case of ectopic pairing between two different 5S sites in the genome is reported, and the significance of ectopic pairing is considered.The author was a Predoctoral Fellow supported by Grant GM 1974 from the National Institute of General Medical Sciences, National Institutes of Health.Contribution from Oak Ridge National Laboratory, operated by the Union Carbide Corporation for the U.S. Energy Research and Development Administration.     

Variability in the molecular organization of the 5S RNA genes among strains of Drosophila melanogaster.

The organization of the 5S RNA cluster has been analyzed in four strains of Drosophila melanogaster by the Southern technique. In some of the strains the 5S RNA cluster appears to be interrupted by an unrelated sequence. In other strains a continuous cluster is present.     

Evolution of the 5 S RNA genes in vertebrates

Summary We have built the phylogenetic tree of Vertebrate 5S RNA using the sequence data of thirteen species belonging to six groups. Evolution of the 5S genes has been very slow in Vertebrates since 90 residues are identical in all 5S RNAs which are presently sequenced.In Amphibians and Teleosts different 5S genes are active in oocytes and in somatic cells. This dual gene system has probably been acquired independently by Amphibians and Teleosts. In Amphibians, the oocyte-type 5S genes have evolved much faster than the somatic-type genes. This is not true in all species since the oocyte-type genes of one Teleost (Tinca tinca) have evolved more slowly than the somatic-type genes.There are in all Vertebrate 5S RNAs five complementary regions which can be base-paired. The sequence data are compatible with the three secondary-structure models that have been proposed for 5S RNA.     

Structural evolution of the Drosophila 5S ribosomal genes

We compare the 5S gene structure from nine Drosophila species. New sequence data (5S genes of D. melanogaster, D. mauritiana, D. sechellia, D. yakuba, D. erecta, D. orena, and D. takahashii) and already-published data (5S genes of D. melanogaster, D. simulans, and D. teissieri) are used in these comparisons. We show that four regions within the Drosophila 5S genes display distinct rates of evolution: the coding region (120 bp), the 5-flanking region (54–55 bp), the 3-flanking region (21–22 bp), and the internal spacer (149–206 bp). Intra- and interspecific heterogeneity is due mainly to insertions and deletions of 6–17-bp oligomers. These small rearrangements could be generated by fork slippages during replication and could produce rapid sequence divergence in a limited number of steps. Correspondence to: M. Wegnez     

A procedure for the cloning and identification of Y-specific middle repetitive sequences in Drosophila hydei

Clones of hybrid plasmids containing moderately and highly repeated sequences of Drosophila hydei exhibit positive autoradiographic signals if hybridized to labeled whole genome DNA. Such clones were screened with labeled male ($\text{X}\text{Y}$) and female ($\text{X}\text{X}$) DNA, and male-specific fragments were identified. Further hybridization of male-specific clones to female $\text{XX}\text{Y}$, and male $\text{X}\text{0}$ DNAs established them as containing Y-specific moderately repeated sequences. Further verification of one particular cloned fragment as Y-specific is presented and possible applications of this procedure are briefly discussed.     

The 5S genes of Drosophila melanogaster.

We have cloned embryonic Drosophila DNA using the poly (dA-DT) connector method (Lobban and Kaiser, 1973) and the ampicillin-resistant plasmid pSF2124 (So, Gill and Falkow, 1975) as a cloning vehicle. Two clones, containing hybrid plasmids with sequences complementary to a 5S RNA probe isolated from Drosophila tissue culture cells, were identified by the Grunstein and Hogness (1975) colony hybridization procedure. One hybrid plasmid has a Drosophila insert which is comprised solely of tandem repeats of the 5S gene plus spacer sequences. The other plasmid contains an insert which has about 20 tandem 5S repeat units plus an additional 4 kilobases of adjacent sequences. The size of the 5S repeat unit was determined by gel electrophoresis and was found to be approximately 375 base pairs. We present a restriction map of both plasmids, and a detailed map of of the5S repeat unit. The 5S repat unit shows slight length and sequence heterogeneity. We present evidence suggesting that the 5S genes in Drosophila melanogaster may be arranged in a single continuous cluster.     

Independent replication of the ribosomal RNA genes in the polytrophic-meroistic ovaries of Calliphora erythrocephala,Drosophila hydei,and Sarcophaga barbata

By filter saturation hybridizations the ribosomal (r)DNA contents of the ovaries Calliphora erythrocephala, Drosophila hydei, and Sarcophaga barbata have been measured in comparison to the rDNA percentages of their diploid brains. The measurements of the ovarian rDNA have been carried out on ovaries where the nurse cells in the distal egg chamber of the ovarioles had reached their highest ploidy level. The diploid rDNA content of each of the respective species was chosen as a 100% standard and the rDNA amounts of the ovaries were related to this 100% level. The results show that the ovaries of C. erythrocephala contain 135% rDNA whereas the rDNA contents in the ovaries of D. hydei and S. barbata are only 51% and 47%, respectively. Measurements carried out on isolated nuclei of the nurse cells and follicle cells in D. hydei show that both have a reduced rDNA content in comparison to the brains (45% and 70%, respectively). The data are discussed in relation to the problem of an rDNA amplification in the germ cells and an rDNA underreplication in polyploid nuclei.     

Organisation of the 5S RNA genes in flax.

The 5S RNA genes of flax [Linum usitatissimum] are arranged as tandem arrays of a 0.35 - 0.37kb repeating sequence. The 5S DNA is extensively methylated at CCGG and CCGG. In contrast to the rDNA, the 5S DNA sequences exhibit both length and sequence heterogeneity. The number of copies of this sequence varies between 117,000 and 49,600 per 2C nucleus in different lines of flax, and does not correlate with the number of rRNA genes.     

Differential replication of satellite DNA in polyploid tissues of Drosophila virilis

Satellite DNA amounts were examined in adult tissues of Drosophila virilis, a species whose DNA contains three prominent satellites. Satellite amounts in DNA from six of the seven tissues were lower than in DNA from diploid (adult brain) tissue. Satellite amounts in adult ovary DNA, however, were equivalent to or greater than diploid levels. When DNA from pupal ovaries was examined, a 30% increase in satellite amounts over diploid levels was found. An RNA-DNA hybridization experiment showed that the ribosomal RNA genes in pupal ovary DNA were under-replicated relative to diploid DNA levels.