Population genetics and phylogenetics of DNA sequence variation at multiple loci within the Drosophila melanogaster species complex

Two regions of the genome, a 1-kbp portion of the zeste locus and a 1.1- kbp portion of the yolk protein 2 locus, were sequenced in six individuals from each of four species: Drosophila melanogaster, D. simulans, D. mauritiana, and D. sechellia. The species and strains were the same as those of a previous study of a 1.9-kbp region of the period locus. No evidence was found for recent balancing or directional selection or for the accumulation of selected differences between species. Yolk protein 2 has a high level of amino acid replacement variation and a low level of synonymous variation, while zeste has the opposite pattern. This contrast is consistent with information on gene function and patterns of codon bias. Polymorphism levels are consistent with a ranking of effective population sizes, from low to high, in the following order: D. sechellia, D. melanogaster, D.mauritiana, and D. simulans. The apparent species relationships are very similar to those suggested by the period locus study. In particular, D. simulans appears to be a large population that is still segregating variation that arose before the separation of D. mauritiana and D. sechellia. It is estimated that the separation of ancestral D. melanogaster from the other species occurred 2.5-3.4 Mya. The separations of D. sechellia and D. mauritiana from ancestral D. simulans appear to have occurred 0.58- 0.86 Mya, with D. mauritiana having diverged from ancestral D. simulans 0.1 Myr more recently than D. sechellia.      

Effect of ethephon and daminozide on the respiration of isolated leaf cells

A combined foliar application of ethephon (2-chloroethylphosphonic acid) at 0.8 kg/ha and daminozide (butanedioic acid mono (2,2 dimethylhydrazide) at 3.2 kg/ha inhibited the vegetative growth of Black Valentine bean (Phaseolus vulgaris L.) without the leaf chlorosis and necrosis caused by ethephon alone. This antagonistic interaction was further evaluated by examining the effect of ethephon and daminozide on respiration and lipid synthesis of isolated leaf cells. Ethephon (1.0 mM) promoted¹⁴CO₂ evolution from cells incubated with¹⁴C-glucose for 14 h by approximately 75%. Characterization of this response with Black Valentine bean mitochondria indicated that the observed stimulation could not be attributed to the existence of a major cyanide insensitive pathway or the possibility of ethephon acting as an uncoupler, which supports the view that ethephon (or ethylene) acts in the cytosol rather than in mitochondria. Daminozide at 30.0 and 60.0 mM inhibited¹⁴CO₂ evolution of isolated cells by 30 and 70%, respectively. Ethephon in combination with daminozide (1.0+60 mM) resulted in a 32% inhibition of respiration. Daminozide (60.0 mM) inhibited the incorporation of¹⁴C-glucose into chloroform-methanol soluble products by 47%, but did not affect the incorporation of¹⁴C-acetate. The results suggest that daminozide may reduce or overcome any stimulatory effect of ethephon on respiration and support an active inhibitory site for daminozide in mitochondria.     

Effect of thyrotropin on the phosphorylation of thyroid chromosomal proteins.

Thyrotropin (TSH) stimulated the phosphorylation of histone H1 in calf thyroid slices but had no effect on other classes of histones. Phosphorylation of total phenol-soluble nonhistone chromosomal proteins was not affected by incubation with TSH. However, when these phenol-soluble nonhistone chromosomal proteins were analysed by two-dimensional gels involving isoelectrofocusing and dodecyl sulfate-polyacrylamide gel electrophoresis, TSH was shown to stimulate the phosphorylation of two specific groups of phosphoproteins with molecular weights between 35,000 and 45,000 and isoelectric points at pH values of 5.4-6.0. This increase in phosphorylation with TSH stimulation was confirmed by quantitative analysis of one-dimensional isoelectrofocusing gels.     

Dynamic Recruitment of CDK5RAP2 to Centrosomes Requires Its Association with Dynein

CDK5RAP2 is a centrosomal protein known to be involved in the regulation of the γ-tubulin ring complex and thus the organization of microtubule arrays. However, the mechanism by which CDK5RAP2 is itself recruited to centrosomes is poorly understood. We report here that CDK5RAP2 displays highly dynamic attachment to centrosomes in a microtubule-dependent manner. CDK5RAP2 associates with the retrograde transporter dynein-dynactin and contains a sequence motif that binds to dynein light chain 8. Significantly, disruption of cellular dynein-dynactin function reduces the centrosomal level of CDK5RAP2. These results reveal a key role of the dynein-dynactin complex in the dynamic recruitment of CDK5RAP2 to centrosomes.