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The rate and pattern of sequence substitutions in the mitochondrial DNA (mtDNA) control region (CR) is of central importance to studies of human evolution and to forensic identity testing. Here, we report a direct measurement of the intergenerational substitution rate in the human CR. We compared DNA sequences of two CR hypervariable segments from close maternal relatives, from 134 independent mtDNA lineages spanning 327 generational events. Ten substitutions were observed, resulting in an empirical rate of 1/33 generations, or 2.5/site/Myr. This is roughly twenty-fold higher than estimates derived from phylogenetic analyses. This disparity cannot be accounted for simply by substitutions at mutational hot spots, suggesting additional factors that produce the discrepancy between very near-term and long-term apparent rates of sequence divergence. The data also indicate that extremely rapid segregation of CR sequence variants between generations is common in humans, with a very small mtDNA bottleneck. These results have implications for forensic applications and studies of human evolution.

Harmful algal blooms (HABs) cause significant economic and ecological damage worldwide. Despite considerable efforts, a comprehensive understanding of the factors that promote these blooms has been lacking, because the biochemical pathways that facilitate their dominance relative to other phytoplankton within specific environments have not been identified. Here, biogeochemical measurements showed that the harmful alga Aureococcus anophagefferens outcompeted co-occurring phytoplankton in estuaries with elevated levels of dissolved organic matter and turbidity and low levels of dissolved inorganic nitrogen. We subsequently sequenced the genome of A. anophagefferens and compared its gene complement with those of six competing phytoplankton species identified through metaproteomics. Using an ecogenomic approach, we specifically focused on gene sets that may facilitate dominance within the environmental conditions present during blooms. A. anophagefferens possesses a larger genome (56 Mbp) and has more genes involved in light harvesting, organic carbon and nitrogen use, and encoding selenium- and metal-requiring enzymes than competing phytoplankton. Genes for the synthesis of microbial deterrents likely permit the proliferation of this species, with reduced mortality losses during blooms. Collectively, these findings suggest that anthropogenic activities resulting in elevated levels of turbidity, organic matter, and metals have opened a niche within coastal ecosystems that ideally suits the unique genetic capacity of A. anophagefferens and thus, has facilitated the proliferation of this and potentially other HABs.

(1999) Proc. Natl. Acad. Sci. U. S. A. 96, 9873-9878). Here we show that the co-repressor mSin3A also interacts with REST. The REST-mSin3A association involves the NH 2 -terminal repressor domain of REST and the paired amphipathic helix 2 domain of mSin3A. REST forms complexes with endogenous mSin3A in mammalian cells, and both mSin3A and CoREST interact with REST in intact mammalian cells. REST repression is blocked in yeast lacking Sin3 and rescued in its presence. In mammalian cells, repression by REST is reduced when binding to mSin3A is inhibited. In mouse embryos, the distribution of mSin3A and REST transcripts is largely coincident. The pattern of CoREST gene expression is more restricted, suggesting that mSin3A is required constitutively for REST repression, whereas CoREST is recruited for more specialized repressor functions.Many genes essential for neuronal functioning, including the brain type II voltage-dependent sodium channel, neuronal growth factors, and neurotransmitter receptors, are repressed in non-neuronal cells by the transcriptional repressor, REST/ NRSF (2-5). Removal of the REST/NRSF binding site (RE1/ NRSE) from the regulatory region of transgenes (6) or expression of a dominant negative form of REST/NRSF in vivo (5) results in aberrant expression of the target genes in non-neural tissues. Deletion of the mouse REST/NRSF gene by homologous recombination results in embryonic lethality (5). Because of its importance in establishing and maintaining the expression pattern of a large number of genes required for neuronal functioning, it was of interest to identify the molecules involved in the repressor mechanism.Previous studies identified two distinct domains in the NH 2 and COOH termini of REST that were both necessary and sufficient to repress brain type II sodium channel reporter genes in transient transfection assays (7) and showed that repression by each of these two domains required distinct titratable factors (8). Recently, repression from the COOH-terminal domain was determined to be mediated by the co-repressor, CoREST (1). We sought to determine whether, in addition to CoREST, mSin3A, a co-repressor for several regulated repressor complexes, might also be involved in REST repression. We found that mSin3A is indeed a functional co-repressor for REST. mSin3A interacts with REST in vitro, in yeast and in intact mammalian cells, and interestingly, the binding site maps to the NH 2 -terminal repressor domain in REST. Furthermore, experiments both in yeast and mammalian cells showed that mSin3A is involved in repressor function. In vivo, the expression patterns of the co-repressors mSin3A and CoREST are distinct. Specifically, in early embryogenesis CoREST exhibits a much more restricted pattern of expression compared with REST and mSin3A, suggesting that the composition of the REST repressor complex during development is dynamic. EXPERIMENTAL PROCEDURES Plasmid ConstructionsYeast Two-hybrid Constructs-LexA-mSin3A was obtained by cloning full-length mSin3A into pBTM116 by standard PCR 1...

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