Unusual sequence element found at the end of an amplicon.

In a polyomavirus-transformed rat cell line, designated LPT, the polyomavirus DNA is integrated into a single chromosomal site. Treatment of LPT cells with carcinogens induces amplification of the integrated virus DNA and flanking cellular sequences. We show that the amplification is arrested within a specific cell DNA segment that maps 1.3 to 1.85 kilobases beyond one virus-cell DNA junction, defined as the left junction. We also present the sequence of an 897-base-pair fragment spanning the arrest site. This fragment contains an unusual sequence element, which consists of two contiguous components, a potential cruciform with stems of 6 base pairs and a d(G-A)27 X d(T-C)27 tract, and maps 1,497 to 1,564 nucleotides beyond the left junction. The possibility that this unusual sequence plays a role in the arrest of the amplification process is discussed.     

Respiration and soluble sugar metabolism in sugar pine embryos

Embroys excised from dormant seeds of sugar pine ( Pinus lambertiana Dougl.) incubated at 25°C (non-dormancy-breaking) or stratified at 5°C (dormancy-breaking) were analyzed to determine temperature effects on the relative activities of respiration and fermentative metabolism, the levels of soluble sugers and the activities of the hydrolytic enzymes, invertase and sucrose synthase, as related to the release of dormancy and germinatio. At 25°C, despite a sharp drop in embryo oxygen uptake after 48 h, a simultaneous decline in acetaldehyde and ethanol concentrations indicated that there was not a shift to fermentative metabolism. The concentrations of soluble sugars showed no treatment effects. Embryo invertase (EC 3.2.1.26) activity changed only slightly at either temperature, while stratification was accompanied by a 4-fold increase in sucrose synthase (EC 2.4.1.13) activity (cleavage direction). Upon transfer of stratified seeds to 25°C, embryo sucrose synthase activity rapidly increased almost 10-fold, with the increase beginning prior to germination, while mvertase activity increased 20-fold, concomitant with germination.     

Characterization of Gypsy Moth (Lymantria dispar) Nuclear Polyhedrosis Virus

Characterization of the proteins and nucleic acid of the gypsy moth nuclear polyhedrosis virus isolated in Ithaca, N.Y. (LdNPV-IT) is presented. A total of 29 viral structural proteins were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis when the virus was isolated in the absence of alkaline protease activity. Fourteen surface envelope viral proteins were identified by lactoperoxidase iodination. Eleven proteins were associated with nucleocapsids prepared by Nonidet P-40 detergent treatment. Distinct alterations of viral proteins were documented when virions were purified in the presence of occlusion body-associated alkaline protease(s). Restriction enzyme digests of viral DNA indicated that this isolate was composed of a large number of genetic variants. On the basis of the major molar fragments resulting from EcoRI, BamHI, BglII, and HindIII digests, the molecular weight of the LdNPV genome was approximately 88 × 10⁶.     

Fibre length and gibberellins A1 and A20 are decreased in Eucalyptus globules by acylcyclohexanedione injected into the stem

Trinexapacethyl (TriEt), an acylcyclohexanedionetype inhibitor of gibberellin (GA) biosynthesis, was applied to 3-year-old Eucalyptus globules saplings by localised injection near the base of each stem. The objective was to alter cambial region GA levels and to study the effects on secondary xylem fibre development. Seven weeks later wood samples, with bark and cambial region intact, were removed 10 and 30 cm above the point of injection. Fusiform cambial cell dimensions were compared with those of fibre-tracheids in the most recently formed 100 um of secondary xylem. Increasing TriEt applications from 5 to 5 000 mg active ingredient significantly reduced average fibre length, and to a lesser extent average fusiform cambial cell length. Also reduced was the number of cells in the cambial zone and the number of differentiating fibres with primary walls. However, no trends were evident for changes in fibre diameter, the proportion of vessel elements or the ratio of cambial ray cells to fusiform cambial cells. Two gibberellins (GA₁ and GA₂₀), indole-3-acetic acid (IAA) and abscisic acid (ABA) were quantified in cambial region tissues by gas chromatographymass spectrometry using stable isotope labelled internal standards. Increasing TriEt application reduced both GA₁ and GA₂₀ levels. Effects on IAA and ABA were not significant, although their levels tended to be lower at the highest TriEt application rate. The elongation of secondary xylem fibres was positively correlated with higher levels of endogenous GA₁ (r_s= 0.74, P < 0.01) and GA₂₀ (r_s= 0.72, P < 0.01). These results support a causal role for GA₁ in cambial cell division. They are also consistent with the hypothesis that the elongation of differentiating secondary xylem fibres in woody an–giosperms is dependent on GA₁ levels in the cambial region.     

Modulation of small conductance calcium-activated potassium channels in C6 glioma cells

Using the patch clamp technique, we have characterized a small conductance, calcium-activated potassium (SK) channel in the C6 glioma cell line. Elevation of cytosolic Ca²⁺ concentration ([Ca²⁺] _i ) by applications of serotonin or ionomycin induced bursts of channel openings recorded in the cell-attached configuration. These channels underlie the serotonin-induced, [Ca²⁺] _i -activated whole-cell K⁺ conductance described previously. [Ca²⁺] _i directly activated SK channels in inside-out patches with a biphasic concentration dependence. Submicromolar [Ca²⁺] _i induced bursts of channel openings with a unitary conductance of about 25 pS, similar to that of the serotonin-induced channels. Supramicromolar [Ca²⁺] _i caused prolonged openings with a unitary conductance of about 35 pS, resulting in a pronounced increase of the average current in patches exposed to [Ca²⁺] _i above 100 m. The two modes of opening reflect the activity of the same SK channel. The channel conductance depended on external K⁺ concentration with K _Dof 5 m. The channel was slightly permeable to cations other than K⁺, with a permeability ratio for K⁺Ca²⁺Na⁺ of 10.0400.030, respectively. ATP was required to maintain channel activity in outside-out patches but was not essential in inside-out patches. The modulation of SK channels in C6 cells by components in their microenvironment may be related to the role of glial cells in controlling the extracellular milieu in the CNS.The authors are grateful to Dr. M. Segal for continuous support, stimulating discussions and criticism throughout the course of this work, to Dr. I. Steinberg for helpful suggestions and to Dr. H. Jarosch, for helping with the Fortran application. N.M.'s research was supported in part by BARD, the U.S.-Israel Binational Agricultural Research and Development Fund, grant no. IS-1670-89RC.     

Rhipicephalus sanguineus: Observations on the parasitic stage on dogs in the Negev Desert of Israel

Sixteen dogs were studied for infestation with R. sanguineus in Kibbutz Ze'elim in the north-western part of the Negev Desert over a period of one year. The mean number of ticks per dog per month was 16.4. The majority of the ticks were adults: males (48.6%) and females (34.4%). The cars and abdomen of the dog were the predilection sites for the ticks. Male ticks were more abundant on the ears, whereas female ticks were more abundant on the ears and the abdomen. A strong correlation between tick numbers and the ambient temperatures was found. The mean percentage of dogs infested in the winter months was 16.6% and increased in the summer months to 34.4%. During winter, ticks were found more often on the ears and head of their hosts whereas in summer they were distributed mainly on the ears, headd and abdomen. The male: female ratio was higher in winter (2.3:1) than in summer (1.1:1).