Temperature-dependent energetics of Chaoborus populations: hypothesis for anomalous distributions in the great lakes of East Africa

Chaoborus, the phantom midge (Insecta, Diptera, Chaoboridae), has a widespread distribution, commonly occurring in lakes and ponds all over the world. In the great lakes region of East Africa Chaoborus is present in Lakes Victoria, Albert, Edward, Malawi and George, but absent from Lakes Tanganyika, Kivu and Turkana. Tropical lakes typically have water temperatures in the range of 22–26 °C year round. Lakes Tanganyika and Kivu have only 20% of their bottom sediments oxygenated during full circulation, contrary to 95–100% in all of the other lakes, excluding Lake Malawi (45%) (Hecky & Kling, 1987). Planktivorous fish are present in all lakes (Lehman, 1995). We hypothesized that the absence of Chaoborus larvae from some lakes of East Africa may be the result of interaction among high temperatures, low oxygen levels, and fish predation.We developed a model to estimate energetic costs for Chaoborus larvae at temperatures greater than 14 °C. We hoped to shed light on the bioenergetics of Chaoborus populations, and the possibility that extant distributions of Chaoborus larvae are the result of energetic constraints.We found that relative respiratory and growth costs of Chaoborus larvae are highest in the early stages of development. We estimated that non-feeding instar I larvae living in 25 °C water will starve to death in less than one day. It is possible that Chaoborus populations are prevented from establishing in certain areas because high energetic costs condemn young larvae to death by either predation or starvation.     

Herpes simplex virus type 1 DNA replication is specifically required for high-frequency homologous recombination between repeated sequences.

Using an assay for recombination that measures deletion of a beta-galactosidase gene positioned between two directly repeated 350-bp sequences in plasmids transiently maintained in COS cells, we have found that replication from a simian virus 40 origin produces a high frequency of nonhomologous recombination. In contrast, plasmids replicating from a herpesvirus origin (oris) in COS cells superinfected with herpes simplex virus type 1 (HSV-1) show high levels of homologous recombination between the repeats and an enhanced recombinogenicity of the HSV-1 a sequence that is not seen during simian virus 40 replication. When the same assay was used to study recombination between 120- to 150-bp repeats in uninfected Vero cells, the level of recombination was extremely low or undetectable (< 0.03%), consistent with the fact that these repeats are smaller than the minimal efficient processing sequence for homologous recombination in mammalian cells. Recombination between these short repeats was easily measurable (0.5 to 0.8%) following HSV-1 infection, suggesting that there is an alteration of the recombination machinery. The frequency of recombination between repeats of the Uc-DR1 region, previously identified as the only segment of the HSV-1 a sequence indispensable for enhanced a-sequence recombination, was not significantly higher than that measured for other short sequences.     

Synthesis of one dimensional tin selenides in supercritical amines

Three new crystalline tin selenide salts have been prepared from the reactions of [PPh₄]₂[Sn(Se₄₃] in supercritical solvents. The starting material pyrolyzes in supercritical acetonitrile to form [PPh₄]₄[Sn₆Se₂₁] (I), and it also reacts with SnSe in supercritical ammonia leading to a mixture of [PPh₄]₄[Sn₃Se₁₁]₂ (II). and [PPh₄]₂[Sn(Se₄)(Se₆)₂] (III). All three compounds have been characterized by single crystal X-ray diffraction. Crystallographic data: for I, C₉₆H₉₀P₄Se₂₁Sn₆, space group triclinic, P-1, A = 18.763(3), B = 24.600(4), C = 13.137(1) Å, = 102.63(1), β = 93.66(1), γ = 108.72(1)°, V = 5544(1) ų, Z = 2, R = 0.0350, R_W = 0.0317: for II, C₉₆H₈₀P₄Se₂₂Sn₆, space group monoclinic P2₁/c, A = 31.500(4), B = 16.572(3), C = 22.352(3) Å, β = 103.53(1)°, V = 11344(3) ų, Z = 4, R = 0.0771, R_W = 0.0664: for III, C₄₈H₄₀P₂Se₁₆Sn, space group monoclinic, C2/c, A = 25.381(2), B = 13.934(4), C = 19.465(3) Å, β = 121.587(8)°, V = 5867(2) ų, Z = 4, R = 0.0807, R_W = 0.0650. One of the compounds, [PPh₄]₂[Sn(Se₄(Se₆₂], is a molecular cluster while the other two complexes [PPh₄]₄[Sn₃Se₁₁]₂ and [PPh₄]₄[Sn₆Se₂₁], are one dimensional tin selenide chains. The structures of the two chains are related and consits of tetrahedral and distorted trigonal bipyramidal tin(IV) centers bridged by Se²⁻, Se₂²⁻ and Se₃²⁻ chains.     

Influences of the paraventricular and suprachiasmatic nuclei and olfactory bulbs on melatonin responses in the golden hamster

Removal of the pineal, or denervation of this gland by superior cervical ganglionectomy, blocks testicular regression in golden hamsters exposed to short photoperiods. Aspiration of the olfactory bulbs or lesions of the suprachiasmatic or paraventricular nuclei of the hypothalamus (SCNx or PVNx) have similar effects. We have examined the effects of these operations on pineal melatonin content and gonadal responses to various patterns of exogenous melatonin in order to examine the roles played by the olfactory bulbs, the SCN, and the PVN in hamster photoperiodism. SCNx and PVNx significantly reduced pineal melatonin content throughout the dark phase, while bulbectomy did not significantly affect melatonin concentrations at the time of the nocturnal peak. Bulbectomy significantly delayed the nightly onset of locomotor activity in hamsters exposed to 14L:10D, but not that of animals housed in 10L:14D. Although bulbectomy reduced the gonadal response to one or three daily injections of melatonin, these individuals exhibited significant testicular regression in response to melatonin as long as injections fell in the evening. In contrast, destruction of the PVN rendered hamsters unresponsive to one daily melatonin injection, but equally responsive to three injections, regardless of the time of day at which these injections were given. Whereas exposure of bulbectomized hamsters to 30 weeks of short days made them refractory to subsequent melatonin challenge, PVNx hamsters remained sensitive to appropriately timed melatonin treatments regardless of their photoperiodic history. Many, but not all hamsters that experienced complete SCN lesions remained sensitive to three daily melatonin injections.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alpha-factor leader sequence-directed transport of Escherichia coli beta-galactosidase in the secretory pathway of Saccharomyces cerevisiae

Summary The constuction of two fused genes is described. One involves the in-frame fusion of the yeast prepro--factor coding sequence, and the Escherichia coli lac Z gene. The second gene fusion utilizes a 103 bp yeast invertase NH₂-terminal coding sequence at the fusion junction of the hybrid gene described above. The gene fusions, under the control of the -factor promoter, expressed active -galactosidase in haploid yeast cells. The activity could be regulated in a temperature-sensitive sir3 mutant. The incorporation of the invertase coding sequence at the MF1-lacZ fusion junction provided significantly higher levels of -galactosidase activity. A substantial quantity of the hybrid proteins generated from the gene fusions was primarily localized in the intracellular membranes of yeast cells, while a processed form could be secreted into the periplasm.A portion of this work appeared in Biotechnology Progress (Das and Shultz 1986) as proceedings of the symposium on Industrial Scale Protein Purification, held at the annual meeting of the Institute of Chemical Engineers in Miami Beach, Fla, USA on November 4, 1986     

Calcium-Dependent Myosin from Insect Flight Muscles

Calcium regulation of the insect actomyosin ATPase is associated with the thin filaments as in vertebrate muscles, and also with the myosin molecule as in mollusks. This dual regulation is demonstrated using combinations of locust thin filaments with rabbit myosin and locust myosin with rabbit actin; in each case the ATPase of the hybrid actomyosin is calcium dependent. The two regulatory systems are synergistic, the calcium dependency of the locust actomyosin ATPase being at least 10 times that of the hybrid actomyosins described above. Likewise Lethocerus myosin also contains regulatory proteins. The ATPase activity of Lethocerus myosin is labile and is stabilized by the presence of rabbit actin. Tropomyosin activates the ATPase of insect actomyosin and the activation occurs irrespective of whether the myosin is calcium dependent or rendered independent of calcium.     

Excision of thymine dimers by proteolytic and amber fragments of E. coli DNA polymerase I

Excision of thymine dimers from specifically incised ultraviolet irradiated DNA by $\text{E. coli}$ DNA polymerase I is stimulated by concurrent DNA synthesis. The 36,000 molecular-weight “small fragment” obtained by limited proteolysis of DNA polymerase I, which retains only the 5′ → 3′ exonuclease activity, also excises thymine dimers, but at one-tenth the rate of the intact enzyme. However, the rate of excision is increased by addition of the “large” 76,000-molecular weight fragment. With the further addition of the 4 deoxynucleoside triphosphates, permitting DNA synthesis to occur, excision approaches rates observed with the intact enzyme. The same result was obtained with a fragment of DNA polymerase I with 5′ → 3′ exonuclease activity that is present uniquely in polymerase I $\text{amber}$ mutants.     

The structural elements responsible for contraction in the ciliateSpirostomum

Summary The surface of the contractile ciliateSpirostomum contains continuous spiral ciliated grooves traversing its length. Bundles of microtubules run parallel to the base of the grooves and appear to be part of a cohesive, semi-rigid cortex. Beneath this, a network of microfilament bundles occurs which is attached to the peristomal membranelle apparatus, also part of the cortex. The possible roles played by these structures during contraction of the organism were examined.During contraction, the entire cortex twists and the spiral arrangement of the grooves and microtubules decreases in pitch and increases in diameter. Simultaneously, the bundles of microfilaments change in distribution and appearance so as to suggest that they are undergoing an active shortening process. Based on these observations, two models for contraction are presented. In one, shortening of the animal arises from a smooth muscle-like contraction of the microfilament network whose attachment to the basal bodies of the membranellar cilia guarantees shortening and widening of the cortex and consequently the whole animal. In the second, a shortening (or sliding) of external microtubules relative to internal ones in the cortical microtubule bundles would result in an increase in diameter, a decrease in pitch, and a decrease in axial length of the bundles, resulting in contraction of the animal. The observations do not allow a choice between these alternatives to be made, and they may not, in fact, be mutually exclusive.