Description of the oöcysts of Eimeria arnyi n. sp. (Apicomplexa: Eimeriidae) from the eastern ringneck snake Diadophis punctatus arnyi (Serpentes: Colubridae)

Coccidian oöcysts recovered from the faeces of eastern ringneck snakes, Diadophis punctatus arnyi, from Kansas, USA were found to represent a previously unreported eimerian. Oöcysts of Eimeria arnyi n. sp. are subspherical, 16.9×15.1 (15–18.5×13.5–16) m, with a thin, single-layered wall and a shape-index (length/width) of 1.1 (1.1–1.3). A micropyle and öocyst residuum are absent but a large polar granule is present. The sporocysts are elongate, 13.2×6.9 (12–14.5×6.5–7) m, with Stieda and substieda bodies and a shape-index of 1.9 (1.7–2.3). Each sporozoite contains one to two anterior and a single posterior refractile bodies. Sporulation was exogenous and complete within four days at 23°C.     

Binding of the gamma-subunit of retinal rod-outer-segment phosphodiesterase with both transducin and the catalytic subunits of phosphodiesterase.

The gamma-subunit of retinal rod-outer-segment phosphodiesterase (PDE-gamma) is a multifunctional protein which interacts directly with both of the catalytic subunits of PDE (PDE alpha/beta) and the alpha-subunit of the retinal G (guanine-nucleotide-binding)-protein transducin alpha (T alpha). We have previously reported that the PDE gamma binds to T alpha at residue nos. 24-45 [Morrison. Rider & Takemoto (1987) FEBS Lett. 222, 266-270]. In vitro this results in inhibition of T alpha GTP/GDP exchange [Morrison, Cunnick, Oppert & Takemoto (1989) J. Biol. Chem. 264, 11671-11681]. We now report that the inhibitory region of PDE gamma for PDE alpha/beta occurs at PDE gamma residues 54-87. This binding results in inhibition of either trypsin-solubilized or membrane-bound PDE alpha/beta. PDE gamma which has been treated with carboxypeptidase Y, removing the C-terminus, does not inhibit PDE alpha/beta, but does inhibit T alpha GTP/GDP exchange. Inhibition by PDE gamma can be removed by T alpha-guanosine 5'-[gamma-thio]triphosphate (GTP[S]) addition to membranes. This results in a displacement of PDE gamma, but not in removal of this subunit from the membrane [Whalen, Bitensky & Takemoto (1990) Biochem. J. 265, 655-658]. These results suggest that low levels of T alpha-GTP[S] can result in displacement of PDE gamma from the membrane in vitro as a GTP[S]-T alpha-PDE gamma complex. Further activation by high levels of T alpha-GTP[S] occurs by displacement of PDE gamma from its inhibitory site on PDE alpha/beta, but not in removal from the membrane.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.