Comparative sequence analysis as a tool for studying the secondary structure of mRNAs.

Analysis of phylogenetically conserved secondary structure has been important in the development of models for the secondary structure of structural RNAs. In this paper, we apply this type of analysis to several families of informational RNAs to evaluate its usefulness in developing secondary structure models for mRNAs and mRNA precursors. We observed many conserved helices in all mRNA groups analyzed. Three criteria were used to identify potential helices which were not conserved solely because of coding sequence constraints, and may therefore be important for the structure and function of the RNA. These results suggest that this approach will be useful in deriving secondary structure models for informational RNAs when used in conjunction with other complementary techniques, and in designing experiments to determine the functional significance of conserved base pairing interactions.     

The ubiquitous localization of type I hexokinase in rat peripheral nerves, smooth muscle cells and epithelial cells

Summary An indirect immunoperoxidase technique has been used to determine the localization of type I hexokinase in a wide variety of Carnoy-fixed, paraffin-embedded rat tissues. The results suggest that the widespread tissue distribution of the isoenzyme is due to its ubiquitous localization in the nervous, smooth muscle and epithelial components of each tissue. The majority of the immunostaining was confined to cells with substantial energy requirements which are probably mainly satisfied through the breakdown of glucose. This observation is consistent with the known predominance of type I hexokinase in the central nervous system and with the regulatory role allotted to it in this tissue.     

Histochemical and immunohistochemical localization of hexokinase isoenzymes in normal rat liver

Summary Histochemical and immunohistochemical procedures have been used to examine the localization of three of the four hexokinase isoenzymes present in the liver of fed female Wistar rats. Distinctive distribution patterns were found for hexokinase type I and glucokinase but hexokinase type II was not detectable. Hexokinase type I was identified in sinusoidal cells and in bile duct epithelia, nerves and arteries in the portal triad. Glucokinase, the major isoenzyme, was confined to parenchymal cells where it was present in much higher amounts in perivenous compared with periportal hepatocytes. Staining within these two zones was not homogeneous and each had a mosaic appearance caused by the presence of a few hepatocytes containing little or no glucokinase amongst the majority of darkly stained cells in perivenous areas and a few darkly stained cells amongst the majority of unstained cells in periportal areas. Hence, hepatocytesin situ are a strikingly heterogeneous population of cells. Their metabolic status cannot be controlled simply by the differential supply of oxygen, substrates and hormones to different regions of the liver acini as proposed in the metabolic zonation model. Phenotypic differences may exist between cells within a given metabolic zone which influence their ability to respond to different environmental conditions.     

Role of actin binding protein phosphorylation in platelet cytoskeleton assembly

Actin binding protein from human blood platelets is shown to exist in the resting platelet as a phosphorylated protein and contains two residues of phosphate per 260,000 kd. Removal of one-half of these residues with E. coli alkaline phosphatase results in the loss of its ability to crosslink F-actin into a low speed sedimentable complex (its cytoskeleton) and to bind to an F-actin affinity column. Thus, phosphorylation-dephosphorylation of ABP may be an important regulatory mechanism by which the platelet regulates its shape via its cytoskeletal structure.     

What do foraging hummingbirds maximize?

Summary Hainsworth and Wolf (1976) reported that under certain conditions hummingbirds made food choices which did not maximize their net rate of energy intake while foraging. They concluded that the birds were not foraging optimally. We show here that their birds probably maximized a different utility function, the net energy per unit volume consumed (NEVC), which appears to be an optimal choice on a time scale longer than that of a foraging bout. Our own experiments with Archilochus colubris support the conclusion that hummingbirds make foraging decisions that maximize NEVC. A simulation model shows that, in nature, NEVC maximization would require fewer foraging trips and visits to fewer flowers per day to balance daily energy budgets. For territorial birds this can lead to smaller territory sizes and reduced costs of territorial defense. Plants that evolutionarily increase corolla length to enhance pollinator specificity need only increase nectar concentration slightly to maintain the same net energy per unit volume consumed (NEVC) by a given hummingbird pollinator.     

Mammalian species richness on islands on the Sunda Shelf,Southeast Asia

Summary A rich mammalian fauna is found on islands that lie on the Sunda Shelf, a continental shelf extending from Vietnam to Borneo and Java that was periodically exposed as dry land during the Pleistocene. The correlation between log of island area and number of species is high (r ²=0.94); the slope of the curve is moderate (z=0.235). Distance from small islands to source areas (=Borneo, Sumatra, and the Malay Peninsula) does not appear to affect species richness, nor does depth of water to source area (a measure of isolation time). A species-area curve for forest reserves of varying sizes on the Malay Peninsula has a low slope (z=0.104); comparison of the mainlaind and island curves indicates that decreasing island area is strongly correlated with increased extinction. Extinction has left reduced but ecologically balanced sets of species on all islands, except that carnivores are under-represented on all but the largest islands. Initial body size and rarity appear to play a significant role in determining the probability of extinction of individual species.     

Antiepileptic effects of amphetamine may require GABA (benzodiazepine) activity

Secondary components of visual evoked potentials (slow negative wave-SNW, and photically-evoked sensory afterdischarge-SAD) are known to be precursors of experimentally activated wave-spike discharges, similar to wave-spikes of petit mal epilepsy. Both SNW and SAD may be potently suppressed wither by amphetamine or GABAergic compounds such as diazepam and sodium valproate. A hypothesis was tested in the present study, that amphetamine-induced suppression of wave-spike discharges may require GABA-benzodiazepine activity for its expression.Electrocortical activity was recorded and averaged in unrestrained albino rats with chronically implanted epicortical electrodes. SNW and SAD obtained in habituated rats in the predrug state were potently suppressed by amphetamine (1 mg/kg, i.p.). Fifteen minutes after amphetamine injection, a challenging drug (metrazol, picrotoxin, convulsant benzodiazepine, Ro 5-3663, or imidazodiazepine, Ro 15-1788) was administered intraperitoneally. Subconvulsive doses of metrazol (10 mg/kg) reversed amphetamine suppression; imidazodiazepine (20 mg/kg) and picrotoxin (1.5 mg/kg) reliably opposed the SNW suppression; convulsant benzodiazepine, Ro 5-3663 (2 mg/kg), showed modest and nonsignificant effect in the same direction. It is proposed that the antiepileptic potency of amphetamine may be associated with its ability, apparently via modulatory effect of norepinephrine, to facilitate the activation of benzodiazepine-GABA receptors.     

Analysis of cloned mRNA sequences encoding subfragment 2 and part of subfragment 1 of alpha- and beta-myosin heavy chains of rabbit heart

Two cardiac myosin heavy chain cDNA clones, pMHC alpha 252 and pMHC beta 174, were constructed using rabbit ventricular mRNA isolated from adult thyrotoxic and normal hearts, respectively. The complete DNA sequences of the 2.2- and 1.4-kilobase inserts of pMHC beta 174 and pMHC alpha 252, respectively, were obtained. The 736 amino acids specified by pMHC beta 174 begin 439 (1.3 kilobases) residues from the heavy chain NH2 terminus and include a 400-amino acid segment of subfragment 1 and the entire subfragment 2 region. Clone pMHC alpha 252 encodes 465 amino acids encompassing all of subfragment 2 and a portion of light meromyosin. Comparison of these two clones revealed extensive sequence overlap which included 1107 nucleotides specifying a 369-amino acid segment corresponding to subfragment 2. Within this region 78 (7%) base and 32 (8.7%) amino acid mismatches were noted. These differences were clustered within discrete regions, with the subfragment 1/subfragment 2 junctional region being particularly divergent. Structural differences between pMHC alpha 252 and pMHC beta 174 indicate that these two clones represent two similar but distinct myosin heavy chain genes whose expression is responsible for ventricular myosin heavy chain isoforms alpha and beta, respectively. The derived amino acid sequences of both clones exhibit extensive homology (greater than 81%) with sequences obtained by direct analysis of adult rabbit skeletal muscle myosin heavy chain protein. The sequences corresponding to the subfragment 2 region are consistent with an alpha-helical conformation with a characteristic 7-residue periodicity in the linear distribution of nonpolar amino acids. Conversely, subfragment 1 sequences specified by pMHC beta 174 suggest a folded highly irregular structure.     

Ecdysteroid levels and integument changes in post-embryonic stages of Anastrepha suspensa

Ecdysteroid levels in larvae and pupae of Anastrepha suspensa (Diptera: Tephritidae) were measured by radioimmunoassay. These levels were correlated with histological changes throughout the development of the post-embryonic stages. Ecdysteroid levels increase rapidly throughout the last-larval instar and on the last day of this stage are 283 pg equivalents of 20-hydroxyecdysone per insect (14.5 ng/g) when wandering behaviour is initiated. At the end of this period the puparium is formed and within 24 h, the ecdysteroid rises to its highest peak (625 pg equivalents of 20-hydroxyecdysone/insect). Larval-pupal apolysis is initiated within 24 h later and the pupal cuticle is then secreted. Two days later, the ecdysteroids reach their lowest levels (75 pg equivalents of 20-hydroxyecdysone/insect or 0.6 ng/g) and most of the larval fat body and other tissues have been histolysed. In 5- to 10-day old pupae ecdysteroid levels again increase and remain relatively high throughout. During this period the larval epidermis is replaced by imaginal epidermis, imaginal discs begin to proliferate and the adult cuticle is secreted. Ecdysteroid levels finally fall 2 days prior to adult emergence. HPLC determinations indicate that 20-hydroxyecdysone is the predominant free ecdysteroid, and along with ecdysone, is readily detectable in all postembryonic stages of this species. An unusually high and unexplained peak of 20-hydroxyecdysone occurs in the pharate adult. This peak probably consists of ecdysone metabolites with retentions similar to that of 20-hydroxyecdysone and to which the antiserum is sensitive.     

The organization of immunoglobulin variable kappa chain genes on mouse chromosome 6

One mouse with a known recombination (NAK) at the Igk locus on chromosome 6 and two new recombinants [B6.PL (7 NS) and B6.PL (85NS)] were examined using a series of probes, each of which is specific for a set of immunoglobulin (Ig) Vk genes. Under high stringency conditions, each probe detects from 1 to 19 Bam HI restriction endonuclease fragments (REFs) in genomic DNA by Southern transfer hybridization techniques. Analysis of the REF patterns indicate that the NAK recombination event occurred within the variable region of Igk. The REF patterns of the two B6.PL congenic mice provided two additional recombination events which could be examined. Although some of the REFs had shared mobility among the parental strains, at least 1 and up to 13 polymorphic REFs were present for a given probe among the NZB and AKR parental strains. The results from the NAK mouse indicate that at least some members of Vk4, Vk8, Vk10, and Vk21 were on one side of the recombination event linked to the Lyt-2 ^a and Igk-Efl ^a alleles of AKR, while the Vk9, Vk11, and Vk24 REF patterns came from the NZB parental strain linked to the Igk-Ef2 ^b (Vk1) allele. The two B6.PL congenics produced a refined map on the Lyt-2, Lyt-3 side of the Vk region. The B6.PL (85NS) mice retained the Vk21 REF pattern of the Lyt-2 ^a, Lyt-3 ^a donor strain PL/J, while displaying the C57BL/6 REF pattern for the other Vk gene groups tested. The B6.PL (75NS) mice retained the REF patterns of PL/J for Vk21 and Ef-1, indicating a third recombination. This indicates the Vk gene order is (Lyt-2; Vk21); Ef-1; (Vk4; Vk8; Vk10); and (Vk9; Vk11; Vk24; Ef-2).