Constant-parameter capture-recapture models

Jolly (1982, Biometrics 38, 301-321) presented modifications of the Jolly-Seber model for capture-recapture data, which assume constant survival and/or capture rates. Where appropriate, because of the reduced number of parameters, these models lead to more efficient estimators than the Jolly-Seber model. The tests to compare models given by Jolly do not make complete use of the data, and we present here the appropriate modifications, and also indicate how to carry out goodness-of-fit tests which utilize individual capture history information. We also describe analogous models for the case where young and adult animals are tagged. The availability of computer programs to perform the analysis is noted, and examples are given using output from these programs.     

Structure of the mammalian CoA transferase from pig heart

Ketoacidosis affects patients who are deficient in the enzyme activity of succinyl-CoA:3-ketoacid CoA transferase (SCOT), since SCOT catalyses the activation of acetoacetate in the metabolism of ketone bodies. Thus far, structure/function analysis of the mammalian enzyme has been predicted based on the three-dimensional structure of a CoA transferase determined from an anaerobic bacterium that utilizes its enzyme for glutamate fermentation. To better interpret clinical data, we have determined the structure of a mammalian CoA transferase from pig heart by X-ray crystallography to 2.5 A resolution. Instrumental to the structure determination were selenomethionine substitution and the use of argon during purification and crystallization. Although pig heart SCOT adopts an alpha/beta protein fold, resembling the overall fold of the bacterial CoA transferase, several loops near the active site of pig heart SCOT follow different paths than the corresponding loops in the bacterial enzyme, accounting for differences in substrate specificities. Two missense mutations found associated with SCOT of ketoacidosis patients were mapped to a location in the structure that might disrupt the stabilization of the amino-terminal strand and thereby interfere with the proper folding of the protein into a functional enzyme.     

The in vivo effect of indomethacin and prostaglandin E2 on ACTH and DBCAMP-induced steroidogenesis in hypophysectomized rats

The level of plasma corticosterone attained in hypophysectomized rats stimulated with ACTH was significantly reduced by pretreatment with indomethacin, an inhibitor of prostaglandin synthesis. This effect was not seen in animals stimulated with dibutyryl cyclic AMP. Intraperitoneal injection of prostaglandin E₂ to indomethacin treated rats restored the normal response to ACTH stimulation. However, PGE₂ itself did not have any significant effect on plasma corticosterone levels. These findings suggest that prostaglandins are involved, perhaps in an allosteric fashion, in the mechanism of action of ACTH.     

The elimination of primer-dimer accumulation in PCR.

We attempted to produce primer-dimers (PDs) from a variety of primers with differing types and extents of complementarity. Where PDs were produced they were cloned and sequenced. We were unable to produce detectable PDs either with individual primers alone or with similar sequence primers even if they had 3'complementarity. These observations led to the hypothesis that a system could be developed whereby the accumulation of PDs in a PCR may be eliminated. We demonstrate a method for the general suppression of PD formation that uses a sequence of additional nucleotides (a Tail) at the 5' ends of amplimers. Tailed amplimers are present at low concentration and only participate during early cycles of PCR. In subsequent PCR cycles, amplification is achieved using a single primer that has the same sequence as that of the Tail portion of the early cycle primers, here we refer to this as a Tag. When products are small, as with PDs, there is a high local concentration of complementary sequences derived from the Tail. This favours the annealing of the complementary ends of a single strand produced by tailed primer interactions and gives rise to 'pan-handle' structures. The formation of these outcompetes the annealing of further Tag primers thereby preventing the accumulation of non-specific PD products. This aids the design of large multiplex reactions and provides a means of detecting specific amplicons directly in the reaction vessel by using an intercalating dye.     

Subunits of succinyl-coenzyme A synthetase: coordination of production in Escherichia coli and discovery of a factor that precludes refolding.

Succinyl-coenzyme A synthetase of Escherichia coli has an alpha 2 beta 2 subunit structure. By measuring reconstituted enzyme activity present after addition of purified alpha or beta subunits to cell extracts followed by refolding, we have shown that extracts contain no significant excess of either subunit species. This equivalence suggests that the expression of the respective structural genes for the subunits is coordinately controlled. The presence of cell extract does not affect the rate or extent of reassembly of the subunits, pointing to a high degree of specificity of mutual recognition by the refolding subunits. In the course of these experiments, we have detected the presence in cell extracts of a low-molecular-weight factor that specifically inactivates unfolded alpha or beta subunits or prevents their reassembly into catalytically active enzyme. Under conditions where the subunits are completely inactivated, the factor has no detectable effect on native or refolded tetrameric enzyme, suggesting that the factor may react only with unfolded protein.