Structural evolution of the Drosophila 5S ribosomal genes

Effects of permissible maximum-contamination levels of VOC mixture in water on total DNA, antioxidant gene expression, and sequences of ribosomal DNA of Drosophila melanogaster

In this study, we aimed to investigate the mutagenic and carcinogenic potential of a volatile organic compound (VOC) mixture with references to the response of D.melanogaster using selected antioxidant gene expressions, RAPD assay and base-pair change of ribosomal 18S, and the internal transcribed spacer, ITS2 rDNA gene sequences. For this purpose, Drosophila melanogaster Oregon R, reared under controlled conditions on artificial diets, were treated with the mixture of thirteen VOCs, which are commonly found in water in concentrations of 10, 20, 50, and 75 ppb for 1 and 5 days. In the random amplified polymorphic DNA (RAPD) assay, band changes were clearly detected, especially at the 50 and 75 ppb exposure levels, for both treatment periods, and the band profiles exhibited clear differences between the treated and untreated flies with changes in band intensity and the loss/appearance of bands. Quantitative real-time PCR (qRT-PCR) analysis of Mn-superoxide dismutase (Mn-SOD), catalase (CAT) and glutathione-synthetase (GS) expressions demonstrated that these markers responded significantly to VOC-induced oxidative stress. Whilst CAT gene expressions increased linearly with increasing concentrations of VOCs and treatment times, the 50- and 75-ppb treatments caused decreases in GS expressions compared to the control at 5 days. Treatment with VOCs at both exposure times, especially in high doses, caused gene mutation of the 18S and the ITS2 ribosomal DNA. According to this research, we thought that the permissible maximum-contamination level of VOCs can cause genotoxic effect especially when mixed.

Characteristics of the nuclear (18S, 5.8S, 28S and 5S) and mitochondrial (12S and 16S) rRNA genes of Apis mellifera (Insecta: Hymenoptera): structure, organization, and retrotransposable elements

As an accompanying manuscript to the release of the honey bee genome, we report the entire sequence of the nuclear (18S, 5.8S, 28S and 5S) and mitochondrial (12S and 16S) ribosomal RNA (rRNA)-encoding gene sequences (rDNA) and related internally and externally transcribed spacer regions of Apis mellifera (Insecta: Hymenoptera: Apocrita). Additionally, we predict secondary structures for the mature rRNA molecules based on comparative sequence analyses with other arthropod taxa and reference to recently published crystal structures of the ribosome. In general, the structures of honey bee rRNAs are in agreement with previously predicted rRNA models from other arthropods in core regions of the rRNA, with little additional expansion in non-conserved regions. Our multiple sequence alignments are made available on several public databases and provide a preliminary establishment of a global structural model of all rRNAs from the insects. Additionally, we provide conserved stretches of sequences flanking the rDNA cistrons that comprise the externally transcribed spacer regions (ETS) and part of the intergenic spacer region (IGS), including several repetitive motifs. Finally, we report the occurrence of retrotransposition in the nuclear large subunit rDNA, as R2 elements are present in the usual insertion points found in other arthropods. Interestingly, functional R1 elements usually present in the genomes of insects were not detected in the honey bee rRNA genes. The reverse transcriptase products of the R2 elements are deduced from their putative open reading frames and structurally aligned with those from another hymenopteran insect, the jewel wasp Nasonia (Pteromalidae). Stretches of conserved amino acids shared between Apis and Nasonia are illustrated and serve as potential sites for primer design, as target amplicons within these R2 elements may serve as novel phylogenetic markers for Hymenoptera. Given the impending completion of the sequencing of the Nasonia genome, we expect our report eventually to shed light on the evolution of the hymenopteran genome within higher insects, particularly regarding the relative maintenance of conserved rDNA genes, related variable spacer regions and retrotransposable elements.

Cerastodermaglaucum5S ribosomal DNA: characterization of the repeat unit, divergence with respect toCerastoderma edule, and PCR–RFLPs for the identification of both cockles

The 5S rDNA repeat unit of the cockle Cerastoderma glaucum from the Mediterranean and Baltic coasts was PCR amplified and sequenced. The length of the units was 539–568 bp, of which 120 bp were assigned to the 5S rRNA gene and 419–448 bp to the spacer region, and the G/C content was 46%–49%, 54%, and 44%–47%, respectively. Two types of units (A and B), differing in the spacer, were distinguished based on the percentage of differences and clustering in phylogenetic trees. A PCR assay with specific primers for each unit type indicated that the occurrence of both units is not restricted to the sequenced individuals. The 5S rDNA units of C. glaucum were compared with new and previously reported sequences of Cerastoderma edule. The degree of variation observed in C. edule was lower than that in C. glaucum and evidence for the existence of units A and B in C. edule was not found. The two cockles have the same coding region but displayed numerous fixed differences in the spacer region and group separately in the phylogenetic trees. Digestion of the 5S rDNA PCR product with the restriction enzymes HaeIII and EcoRV revealed two RFLPs useful for cockle identification.Key words: Cerastoderma, cockle identification, 5S ribosomal DNA, nontranscribed spacer variation, PCR-RFLP.

The 5S rDNA of mussels Mytilus galloprovincialis and M. edulis: sequence variation and chromosomal location

The 5S ribosomal DNA of the mussels Mytilus galloprovincialis and M. edulis was amplified by PCR using contiguous primers. The most general 5S rDNA amplification pattern consisted of several products in both mussels. Two main PCR products of about 250 bp and 760 bp were cloned and sequenced, revealing two classes of 5S rDNA units. These were characterized as containing an identical coding region of 119 bp but with highly divergent spacers. Clones of each unit type exhibited minimal differences except those of the large unit of M. edulis. The sequences analysed of the two mussels possess the same coding region and only six fixed base changes on the spacers. FISH, carried out with specific probes, consistently showed hybridization signals on the largest metacentric pair (two differentiated sites) and with variable frequency on two other metacentric pairs (one site on each pair). Differences in the 5S rDNA distribution between both mussels were not found. In M. edulis, chromosomes carrying 18S-28S rDNA were also identified by FISH. These correspond to two submetacentric-subtelocentric pairs, as was previously reported in M. galloprovincialis, demonstrating that the two rDNA multigene families are located on different chromosome pairs in these mussels.

Polytene chromosomes as indicators of phylogeny in several species groups of Drosophila

BACKGROUND

Polytene chromosome banding patterns have long been used by Drosophila evolutionists to infer degree of relatedness among taxa. Recently, nucleotide sequences have preempted this traditional method. We place the classical Drosophila evolutionary biology tools of polytene chromosome inversion analysis in a phylogenetic context and assess their utility in comparison to nucleotide sequences.

RESULTS

A simultaneous analysis framework was used to examine the congruence of the chromosomal inversion data with more recent DNA sequence data in four Drosophila species groups - the melanogaster, virilis, repleta, and picture wing. Inversions and nucleotides were highly congruent with one another based on incongruence length difference and partitioned Bremer support values. Inversion phylogenies were less resolved because of fewer numbers of characters. Partitioned Bremer supports, corrected for the number of characters in each matrix, were higher for inversion matrices.

CONCLUSIONS

Polytene chromosome data are highly congruent with DNA sequence data and, when placed in a simultaneous analysis framework, are shown to be more information rich than nucleotide data.

Double-strand break repair in yeast requires both leading and lagging strand DNA polymerases

Mitotic double-strand break (DSB)-induced gene conversion at MAT in Saccharomyces cerevisiae was analyzed molecularly in mutant strains thermosensitive for essential replication factors. The processivity cofactors PCNA and RFC are essential even to synthesize as little as 30 nucleotides following strand invasion. Both PCNA-associated DNA polymerases delta and epsilon are important for gene conversion, though a temperature-sensitive Pol epsilon mutant is more severe than one in Pol delta. Surprisingly, mutants of lagging strand replication, DNA polymerase alpha (pol1-17), DNA primase (pri2-1), and Rad27p (rad27 delta) also greatly inhibit completion of DSB repair, even in G1-arrested cells. We propose a novel model for DSB-induced gene conversion in which a strand invasion creates a modified replication fork, involving leading and lagging strand synthesis from the donor template. Replication is terminated by capture of the second end of the DSB.