Endless forms most stupid,icky, and small: The preponderance of noncharismatic invertebrates as integral to a biologically sound view of life

Big, beautiful organisms are useful for biological education, increasing evolution literacy, and biodiversity conservation. But if educators gloss over the ubiquity of streamlined and miniaturized organisms, they unwittingly leave students and the public vulnerable to the idea that the primary evolutionary plot of every metazoan lineage is “progressive” and "favors" complexity. We show that simple, small, and intriguingly repulsive invertebrate animals provide a counterpoint to misconceptions about evolution. Our examples can be immediately deployed in biology courses and outreach. This context emphasizes that chordates are not the pinnacle of evolution. Rather, in the evolution of animals, miniaturization, trait loss, and lack of perfection are at least as frequent as their opposites. Teaching about invertebrate animals in a “tree thinking” context uproots evolution misconceptions (for students and the public alike), provides a mental scaffold for understanding all animals, and helps to cultivate future ambassadors and experts on these little‐known, weird, and fascinating taxa.     

Octanoylation of the lipoyl domains of the pyruvate dehydrogenase complex in a lipoyl-deficient strain of Escherichia coli

The overexpression of a subgene encoding a hybrid lipoyl domain of the dihydrolipoamide acetyltransferase component of the pyruvate dehydrogenase complex of Escherichia coli has previously been shown to result in the formation of lipoylated and unlipoylated products. Overexpression of the same subgene in a lipoic acid biosynthesis mutant growing under lipoate-deficient conditions has now been shown to produce domains modified by octanoylation as well as unmodified domains. It was concluded from the mass of a lipoyl-binding-site peptide that the modification involves N6-octanoylation of the lysine residue (Lys244) that is normally lipoylated, and this was confirmed by the trypsin-insensitivity of the corresponding Lys244-Ala-245 bond, and the absence of modification in a mutant domain in which Lys244 is replaced by Gln. This novel protein modification raises interesting questions concerning the pathway of lipoic acid biosynthesis and the mechanism of enzyme lipoylation.     

A spectrophotometric assay for 6-phosphogluconolactonase involving the use of immobilized enzymes to prepare the labile 6-phosphoglucono-delta-lactone substrate.

We report the development of a new spectrophotometric assay for 6-phosphogluconolactonase. The labile substrate 6-phosphoglucono-delta-lactone is prepared from glucose 6-phosphate by enzymes co-immobilized on Sepharose beads. The assay has the advantages of high sensitivity for routine determination of enzyme activity and allows determination of both Km and Vmax. from a single assay. A method for estimating the contribution of spontaneous hydrolysis to total hydrolysis is described. This assay overcomes the problems encountered with all previous assays.     

The interaction of troponin-I with the N-terminal region of actin

The interaction between troponin-I and actin that underlies thin-filament regulation in striated muscle has been studied using proton magnetic resonance spectroscopy. A restricted portion of skeletal muscle troponin-I (residues 96-116) has previously been shown to be capable of inhibiting the MgATPase activity of actomyosin in a manner enhanced by tropomyosin [Syska et al. (1976) Biochem. J. 153, 375-387]. On the basis of homologous spectral effects for signals of specific groups observed in different complexes formed using the native proteins and a variety of defined peptides, it is concluded that the segment of troponin-I which has inhibitory activity interacts with the N-terminal region of actin. The surface of contact of the inhibitory segment of troponin-I with actin involves two regions of the N-terminal of actin. These are located between residues 1-7 and 19-44. The data are discussed in the context of a structural mechanism for the inhibition of myosin ATPase activation.     

Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans

Recent studies of mitochondrial DNA (mtDNA) variation in mammals and Drosophila have shown an excess of amino acid variation within species (replacement polymorphism) relative to the number of silent and replacement differences fixed between species. To examine further this pattern of nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5 genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans. Of interest are the frequency spectra of silent and replacement polymorphisms, and potential variation among genes and taxa in the departures from neutral expectations. The Drosophila ND3 and ND5 data show no significant excess of replacement polymorphism using the McDonald-Kreitman test. These data are in contrast to significant departures from neutrality for the ND3 gene in mammals and other genes in Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however, both Drosophila and human mtDNA show very significant excesses of amino acid polymorphism. Silent polymorphisms at ND5 show a significantly higher variance in frequency than replacement polymorphisms, and the latter show a significant skew toward low frequencies (Tajima's D = -1.954). These patterns are interpreted in light of the nearly neutral theory where mildly deleterious amino acid haplotypes are observed as ephemeral variants within species but do not contribute to divergence. The patterns of polymorphism and divergence at charge-altering amino acid sites are presented for the Drosophila ND5 gene to examine the evolution of functionally distinct mutations. Excess charge-altering polymorphism is observed at the carboxyl terminal and excess charge-altering divergence is detected at the amino terminal. While the mildly deleterious model fits as a net effect in the evolution of nonrecombining mitochondrial genomes, these data suggest that opposing evolutionary pressures may act on different regions of mitochondrial genes and genomes.