The novel flightless-I gene brings together two gene families, actin- binding proteins related to gelsolin and leucine-rich-repeat proteins involved in Ras signal transduction

The Drosophila melanogaster gene flightless-I, involved in gastrulation and muscle degeneration, has Caenorhabditis elegans and human homologues. In these highly conserved genes, two previously known gene families have been brought together, families encoding the actin- binding proteins related to gelsolin and the leucine-rich-repeat (LRR) group of proteins involved in protein-protein interactions. Both these gene families exhibit characteristics of molecular changes involving replication slippage and exon shuffling. Phylogenetic analyses of 19 amino acid sequences of 6 related protein types indicate that actin- associated proteins related to gelsolin are monophyletic to a common ancestor and include flightless proteins. Conversely, comparison of 24 amino acid sequences of LRR proteins including the flightless proteins indicates that flightless proteins are members of a structurally related subgroup. Included in the flightless cluster are human and mouse rsp-1 proteins involved in suppressing v-Ras transformation of cells and the membrane-associated yeast (Saccharomyces cerevisae) adenylate cyclase whose analogous LRRs are required for interaction with Ras proteins. There is a strong possibility that ligands for this group could be related and that flightless may have a similar role in Ras signal transduction. It is hypothesized that an ancestral monomeric gelsolin precursor protein has undergone at least four independent gene reorganization events to account for the structural diversity of the extant family of gelsolin-related proteins and that gene duplication and exon shuffling events occurred prior to or at the beginning of multicellular life, resulting in the evolution of some members of the family soon after the appearance of actin-type proteins.      

Magnesium-induced inner membrane aggregation in heart mitochondria: prevention and reversal by carboxyatractyloside and bongkrekic acid

Mg(2+) at an optimal concentration of 2mM (ph 6.5) induces large increases (up to 30 percent) in the optical density of bovine heart mitochondria incubated under conditions of low ionic strength (< approx. 0.01). The increases are associated with aggregation (sticking together) of the inner membranes and are little affected by changes in the energy status of the mitochondria. Virtually all of a number of other polyvalent cations tested and Ag(+) induce increases in mitochondrial optical density similar to those induced by Mg(2+), their approximate order of concentration effectiveness in respect to Mg(2+) being: La(3+) > Pb(2+) = Cu(2+) > Cd(2+) > Zn(2+) > Ag(+) > Mn(2+) > Ca(2+) > Mg(2+). With the exception of Mg(2+), all of these cations appear to induce swelling of the mitochondria concomitant with inner membrane aggregation. The inhibitors of the adenine nucleotide transport reaction carboxyatratyloside and bongkrekic acid are capable of preventing and reversing Mg(2+)-induced aggregation at the same low concentration required for complete inhibition of phosphorylating respiration, suggesting that they inhibit the aggregation by binding to the adenine nucleotide carrier. The findings are interpreted to indicate (a) that the inner mitochondrial membrane is normally prevented from aggregating by virtue of its net negative outer surface change, (b) that the cations induce the membrane to aggregate by binding at its outer surface, decreasing the net negative charge, and (c) that carboxyatractyloside and bongkrekic acid inhibit the aggregation by binding to the outer surface of the membrane, increasing the net negative charge.     

Rates and patterns of mitochondrial DNA sequence evolution in fringilline finches (fringilla spp.) and the greenfinch (Carduelis chloris)

Rates and patterns of evolution in partial sequences of five mitochondrial genes (cytochrome b, ATPase 6, NADH dehydrogenase subunit 5, tRNA(Glu), and the control region) were compared among taxa in the passerine bird genera Fringilla and Carduelis. Rates of divergence do not vary significantly among genes, even in comparisons with the control region. Rate variation among lineages is significant only for the control region and NADH dehydrogenase subunit 5, and patterns of variation are consistent with the expectations of neutral theory. Base composition is biased in all genes but is stationary among lineages, and there is evidence for directional mutation pressure only in the control region. Despite these similarities, patterns of substitution differ among genes, consistent with alternative regimes of selective constraint. Rates of nonsynonymous substitution are higher in NADH dehydrogenase subunit 5 than in other protein-coding genes, and transitions exist in elevated proportions relative to transversions. Transitions appear to accumulate linearly with time in tRNA(Glu), and despite exhibiting the highest overall rate of divergence among species, there are no transversional changes in this gene. Finally, for resolving phylogenetic relationships among Fringilla taxa, the combined protein-coding data are broadly similar to those of the control region in terms of phylogenetic informativeness and statistical support.