Cyromazine resistance in Drosophila melanogaster (Diptera: Drosophilidae) generated by ethyl methanesulfonate mutagenesis.

Flies resistant to cyromazine (CGA-72662) were selected in susceptible laboratory populations of Drosophila melanogaster (Meigen) treated with ethyl methane-sulfonate after growth on cyromazine concentrations > LC99. Two resistant lines were obtained. In each case, resistance was a result of a mutation in a single, but different, gene. The resistance genes, designated Rst(2)Cyr and Rst(3)Cyr, were localized to map positions 64 on chromosome II and 47 on chromosome III, respectively. Concentration-mortality analysis of each mutant revealed that both genes conferred a low level (< 5 times) of resistance to cyromazine. Rst(2)Cyr produced LC99s of 1.3 x 10(-4)% (wt/vol) for heterozygotes and 2.7 x 10(-4)% for homozygotes; Rst(3)Cyr values were 1.6 x 10(-4) and 1.8 x 10(-4)%, respectively. These values compare with an LC99 of 5 x 10(-5)% for wild-type. The role of D. melanogaster as a model for insecticide resistance studies is discussed, especially the comparison of laboratory-generated cyromazine resistance in D. melanogaster with field resistance in Musca domestica L.

Organisation and sequence analysis of nuclear-encoded 5s ribosomal RNA genes in cryptomonad algae.

Southern hybridisation, polymerase chain reaction (PCR), and nucleotide sequence, data indicate that the 5s ribosomal RNA (rRNA) gene is linked to the main rRNA gene repeat in the nuclear genome of four cryptomonad algae (Rhinomonas pauca, Storeatula major, Komma caudata, and isolate Cs 134). The 5s gene is apparently transcribed in the same direction as the large and small subunit rRNA genes. The intergenic spacer between the 5s gene and the large subunit rRNA gene exhibits length and sequence polymorphism among the different species. Cryptomonads contain two different eukaryotic genomes: the host nucleus and the nucleus of a eukaryotic endosymbiont. Mapping experiments with isolated chromosomes of the host and endosymbiont genomes showed that the intergenic spacer between the large subunit and the 5s rRNA gene, which was amplified from total DNA by PCR, was derived from the host nuclear genome.

The 5S ribosomal RNA gene is linked to large and small subunit ribosomal RNA genes in the oomycetes, Phytophthora vignae, P. cinnamomi, P. megasperma f.sp. glycinea and Saprolegnia ferax.

Southern hybridization and polymerase chain reaction data indicate that the 5S ribosomal RNA gene is linked to the ribosomal RNA gene repeat unit in the oomycetes, Phytophthora vignae, P. cinnamomi, P. megasperma f.sp. glycinea and Saprolegnia ferax, and is apparently transcribed in the same direction as the large and small subunit ribosomal RNA genes. The polymerase chain reaction has been used to amplify all components of the entire ribosomal RNA gene repeat unit for each of these oomycetes. The total size of all amplified products is identical to the size of the ribosomal RNA gene repeat unit, as determined by Southern analysis.

Evidence that an amoeba acquired a chloroplast by retaining part of an engulfed eukaryotic alga.

Chlorarachniophytes are amoeboid algae with unusual chloroplasts. Instead of the usual two membranes that surround the chloroplasts of plants, green algae, and red algae, the chloroplasts of chlorarachniophytes have four bounding membranes. The extra membranes may reflect an unusual origin of chlorarachniophyte chloroplasts. Rather than inheriting the organelle directly from their ancestors, chlorarachniophytes may have adopted the chloroplast of an algal cell ingested as prey. Parts of the algal cell are postulated to remain within the amoeba as a reduced eukaryotic endosymbiont [Hibberd, D. J. & Norris, R. E. (1984) J. Phycol. 20, 310-330]. A small nucleus-like structure, proposed to be a vestige of the endosymbiont's nucleus, is located in a space between the second and third chloroplast membranes. We cloned and sequenced nuclear-type rRNA genes from chlorarachniophytes and found two highly divergent genes. In situ hybridization shows that one gene is expressed by the amoebal (host) nucleus and the other is expressed by the putative endosymbiont nucleus, suggesting that the latter is indeed a foreign genome. Transcripts from the endosymbiont gene accumulate in the small cytoplasmic compartment between the second and third chloroplast membranes, which we believe to be the remnant cytoplasm of the endosymbiont. Using the endosymbiont gene as a probe, we identified three small chromosomes belonging to the endosymbiont nucleus. This knowledge should allow a detailed molecular analysis of the role of the endosymbiont's genome and cytoplasm in the partnership.

Mitochondrial DNA sequences in ancient Australians: Implications for modern human origins.

DNA from ancient human remains provides perspectives on the origin of our species and the relationship between molecular and morphological variation. We report analysis of mtDNA from the remains of 10 ancient Australians. These include the morphologically gracile Lake Mungo 3 [ approximately 60 thousand years (ka) before present] and three other gracile individuals from Holocene deposits at Willandra Lakes (<10 ka), all within the skeletal range of living Australians, and six Pleistocene/early Holocene individuals (15 to <8 ka) from Kow Swamp with robust morphologies outside the skeletal range of contemporary indigenous Australians. Lake Mungo 3 is the oldest (Pleistocene) "anatomically modern" human from whom DNA has been recovered. His mtDNA belonged to a lineage that only survives as a segment inserted into chromosome 11 of the nuclear genome, which is now widespread among human populations. This lineage probably diverged before the most recent common ancestor of contemporary human mitochondrial genomes. This timing of divergence implies that the deepest known mtDNA lineage from an anatomically modern human occurred in Australia; analysis restricted to living humans places the deepest branches in East Africa. The other ancient Australian individuals we examined have mtDNA sequences descended from the most recent common ancestor of living humans. Our results indicate that anatomically modern humans were present in Australia before the complete fixation of the mtDNA lineage now found in all living people. Sequences from additional ancient humans may further challenge current concepts of modern human origins.