Origins of replication: timing and chromosomal position

Several new methods have been used to localize replication initiation sites in mammalian chromosomes. The results of these studies argue strongly for the presence of defined sequence elements that function much like the origins in the genomes of simple microorganisms. However, relatively disparate results from in vivo and in vitro studies suggest that initiation reactions in mammalian chromosomes may have unique features, possibly related to a more complicated chromosomal architecture.

Acute effects of oral pyridostigmine bromide on conditioned operant performance in rats

Pyridostigmine bromide (Pyr), the current drug of choice in the management of myasthenia gravis, has been suggested for use in Alzheimer's dementia, and as a prophylactic treatment for intoxication with organophosphate cholinesterase inhibitors. The present study was undertaken to evaluate the dose-response and time-course effects of acute oral administration of Pyr over a broad dose range (3-40 mg/kg) on the lever pressing of rats maintained under a multiple fixed-ratio (FR-20) time-out schedule of reinforcement for water reward. The drug produced a dose-dependent biphasic response depression in the overall rate of FR responding. Low doses of Pyr (less than or equal to 12 mg/kg) that caused no gross signs of toxicity only moderately decreased rates of responding, primarily due to a decrease in response rates. Whereas high doses of Pyr (greater than 24 mg/kg) which produced overt signs of peripheral cholinergic intoxication markedly suppressed overall responding, primarily due to cessation of responding. The lowest effective dose of performance disruption was 6 mg/kg, and the ED50 was calculated as 23.3 (17.9-28.7) mg/kg. The time-course data of performance disruption showed that low doses of Pyr (less than or equal to 12 mg/kg) had an onset latency within 40-80 min and a duration of 20-80 min, whereas high doses (greater than or equal to 24 mg/kg) had an onset latency of 20-40 min and a duration greater than 80 min. These results suggest the recommended human therapeutic or prophylactic regimen of 30-120.mg Pyr, orally taken each 8 hours, might adversely affect behavioral performance.

Simplified analysis and structural design for ridge mos optical waveguides

A simplified method is presented for analyzing the optical characteristics of ridge MOS optical waveguides. Equations are derived for calculating the effective refractive indices and the absorption loss coefficients of the E(x)(pq) modes. The computations are performed for air-Au-air/SiO(2)/GaAs/AlGaAs ridge MOS waveguides. To achieve single-mode propagation with low absorption loss, appropriate selection of the structural parameters for this kind of waveguide is discussed.

The IS10 antisense RNA blocks ribosome binding at the transposase translation initiation site

Transposase (tnp) expression from insertion sequence IS10 is controlled, in part, by an antisense RNA, RNA-OUT, which pairs to the translation initiation region of the tnp mRNA, RNA-IN. Genetic experiments suggest that control occurs post-transcriptionally. Here, we present evidence that bears on the control mechanism. Specific ribosome binding at the tnp translation initiation site is demonstrated in vitro. Two mutations that alter tnp translation in vivo are shown to have corresponding effects in vitro. Most importantly, RNA-OUT/RNA-IN pairing is shown to block ribosome binding. In conjunction with the work described in the accompanying paper, we propose that inhibition of ribosome binding also occurs in vivo, and that it is sufficient to account for control. Implications for translational control in analogous systems are discussed.

Multiple origins of replication in the dihydrofolate reductase amplicons of a methotrexate-resistant chinese hamster cell line

We recently showed that replication initiates in the early S period at two closely spaced zones in the 240-kilobase (kb) dihydrofolate reductase (DHFR) amplicon of the methotrexate-resistant Chinese hamster ovary cell line CHOC 400. Both of these initiation loci (ori-beta and ori-gamma) have previously been cloned in a recombinant cosmid. In this study, we identified a third early-firing initiation locus (ori-alpha) in the much larger DHFR amplicon of the independently isolated methotrexate-resistant Chinese hamster cell line DC3F-A3/4K (A3/4K). We describe the molecular cloning of this newly identified locus and demonstrate by chromosomal walking that ori-alpha lies approximately 240 kb upstream from ori-beta. Using overlapping cosmid clones for more than 450 kb of DNA sequence from this region of the DHFR domain, we have monitored the replication pattern of the amplicons in synchronized A3/4K cells. These studies suggest that ori-alpha, ori-beta, and ori-gamma are the only early-firing initiation sites in this 450-kb sequence. In addition, we have been able to roughly localize the termini between ori-alpha and ori-beta and between ori-alpha and the next origin in the 5' direction. Thus, we have now isolated the equivalent of three early-firing replicons (including their origins) from a well-characterized chromosomal domain. With these tools, it should be possible to determine those properties that are shared by the origins and termini of different replicons and which are therefore likely to be functionally significant.

[A study on pathogen antigen and serodiagnosis of Malleus and Melioidosis with McAbs]

A study on pathogen antigen and serodiagnosis of Malleus and Mlioidosis was made with McAbs which are against Ps. mallei or Ps. pseudomallei. The results showed that (1) Ps. mallei and Ps. pseudomallei express different surface antigen types respectively, and there are antigen overlapping in some degree between them; (2) Epitope 2D4 is common to Ps. mallei and Ps. pseudomallei; (3) The antibody which is similar to McAbs 4D4 or 1A9 might be a common serum antibody of Malleus and Melioidosis; and (4) McAb 3A1 is a high specific one which reacts with Ps. pseudomallei only, and with it, it is possible to resolve the immunological problem of distinguishing diagnosis between Malleus and Melioidosis.

Effect of the radioprotector WR-2721 on operant behavior in the rat

The effect of WR-2721 on performance maintained by a fixed-ratio 20 (FR-20) schedule for water reinforcement was studied in male Sprague-Dawley rats. Graded doses of WR-2721 (range 25-100 mg/kg) were administered IP immediately prior to a 60 min test session. WR-2721 had a dose dependent monotonic disruptive effect on FR responding, with significant effects at doses of 50, 75 and 100 mg/kg. WR-2721 also decreased postsession water consumption, but only one significant effect at the highest dose (100 mg/kg). Both slopes of the dose-response regression line are parallel in effect. These data indicate that WR-2721 may affect drinking motivation, which could disrupt operant performance, and WR-2721 affects motor behavior at lower doses than those that depress "motivation" to drink. The log dose-probit analysis on the all-or-none disruptive pattern of pause of responding observed from cumulative records disclosed that the slope of this regression line (s = 1.11) was also almost identical to that of reinforcer decrement analyzed from graded dose-response relationship (s = 1.14) and shared the same estimated ED50's (58.5 and 55.6 mg/kg, respectively). A preliminary study using a variety of pharmacological interventions was also carried out to ascertain if the general functional gastrointestinal disorders produced by WR-2721 may subserve the behavioral deficits. Subcutaneous pretreatments with various selective, peripherally active, gastroprotective drugs [cimetidine (30 and 60 mg/kg), pirenzepine (5 and 10 mg/kg) and domperidone (1, 5 and 10 mg/kg)] 30 min prior to challenge with WR-2721 at dose of 100 mg/kg, demonstrated that these drugs did not yield any apparent significant attenuative effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Ortho-iodosobenzoic acid: its acute toxicity and neurobehavioral effects in mice

o-Iodosobenzoic acid (IBA), in a surfactant micellar medium, is a rapid and efficient catalyst for the hydrolysis of organophosphate (OP) esters. Since little is known about the toxicity of IBA, a primary screen of neurobehavioral toxicity was evaluated in male ICR mice. IBA was administered intraperitoneally in a pH 7.4 phosphate buffer solution containing 8% dimethylformamide. The predominant overt signs of toxicity included an immediate and transient writhing reflex and/or persistent spasmodic myotwitching of the abdomen, and conspicuous suppression of orienting/exploratory behavior and emotional defecation. The dose ranges for ED50 of writhing response, suppression of rearing and spontaneous motor activity overlapped at levels of about one-tenth the acute LD50, 742 (633-856) mumol/kg, being 94.9 (74.5-122.5), 69.8 (47.9-105.4) and 71.1 (49.9-101.3) mumol/kg, respectively; the dose ranges for ED50 of abdominal myotwitching and depression of emotional defecation in a novel environment also overlapped but at levels of about one-fifth the acute LD50, being 138.4 (115.3-167.2) and 146.2 (110.7-196.3) mumol/kg, respectively. Morphine (1.25-10 mg/kg s.c.) antagonized the IBA-induced writhing response and abdominal myotwitching in a dose-dependent manner, with a PD50 of 4.2 and 4.9 mg/kg, respectively. The present report demonstrates that acute intraperitoneal administration of IBA produces an intriguing, non-specific behavioral syndrome, probably resulting from nociceptive stimulation. This implies that IBA might be irritating to the skin and mucosa.

The dihydrofolate reductase amplicons in different methotrexate-resistant Chinese hamster cell lines share at least a 273-kilobase core sequence, but the amplicons in some cell lines are much larger and are remarkably uniform in structure

We have previously cloned and characterized two different dihydrofolate reductase amplicon types from a methotrexate-resistant Chinese hamster ovary cell line (CHOC 400). The largest of these (the type I amplicon) is 273 kilobases (kb) in length. In the present study, we utilized clones from the type I amplicon as probes to analyze the size and variability of the amplified DNA sequences in five other independently isolated methotrexate-resistant Chinese hamster cell lines. Our data indicated that the predominant amplicon types in all but one of these cell lines are larger than the 273-kb type I sequence. In-gel renaturation experiments as well as hybridization analysis of large SfiI fragments separated by pulse-field gradient gel electrophoresis showed that two highly resistant cell lines (A3 and MK42) have amplified very homogeneous core sequences that are estimated to be at least 583 and 653 kb in length, respectively. Thus, the sizes of the major amplicon types can be different in different drug-resistant Chinese hamster cell lines. However, there appears to be less heterogeneity in size and sequence arrangement within a given methotrexate-resistant Chinese hamster cell line than has been reported for several other examples of DNA sequence amplification in mammalian systems.

Organization and genesis of dihydrofolate reductase amplicons in the genome of a methotrexate-resistant Chinese hamster ovary cell line

We have recently isolated overlapping recombinant cosmids that represent the equivalent of two complete dihydrofolate reductase (dhfr) amplicon types from the methotrexate-resistant Chinese hamster ovary (CHO) cell line CHOC 400. In the work described in this report, we used pulse-field gradient gel electrophoresis to analyze large SfiI restriction fragments arising from the amplified dhfr domains. The junction between the 260-kilobase type I amplicons (which are arranged in head-to-tail configurations in the genome) has been localized, allowing the construction of a linear map of the parental dhfr locus. We also show that the 220-kilobase type II amplicons are arranged as inverted repeat structures in the CHOC 400 genome and arose from the type I sequence relatively early in the amplification process. Our data indicate that there are a number of minor amplicon types in the CHOC 400 cell line that were not detected in previous studies; however, the type II amplicons represent ca. 75% of all the amplicons in the CHOC 400 genome. Both the type I and type II amplicons are shown to be composed entirely of sequences that were present in the parental dhfr locus. Studies of less resistant cell lines show that initial amplicons can be larger than those observed in CHOC 400. Once established, a given amplicon type appears to be relatively stable throughout subsequent amplification steps. We also present a modification of an in-gel renaturation method that gives a relatively complete picture of the size and variability of amplicons in the genome.

Occlusion of bridging or avulsed retinal vessels by repeated photocoagulation

A technique is described for occlusion of bridging vessels associated with retinal breaks, and recurring vitreous hemorrhage. Argon laser photocoagulation, applied around and to the vessel in repeated sessions, produces scarring and progressive thinning of the retina until laser energy absorbed in the deep pigmented layers can reach the vessel and occlude it. Seventeen patients presenting with vitreous hemorrhage from bridging vessels were treated. Vitreous hemorrhage recurred in only two patients, one of whom had not returned for completion of treatment. The authors conclude that repeated argon laser photocoagulation is a safe, simple, and effective method for preventing recurrent vitreous hemorrhage from bridging vessels.

Relationship between radioprotective and neuromotor effects of S-2(3-aminopropyl-amino)ethylphosphorothioate (WR-2721) in mice

The radioprotective and neuromotor effects of WR-2721 were studied in male albino ICR strain mice. The protective activity was evaluated by graded doses of WR-2721 (50-400 mg/kg, IP) against whole body 60Co gamma irradiation at a single maximal lethal threshold dose rad (i.e., 1250 rad). The neuromotor effects of the drug were assayed by its action, at the same dose range as used in the protection assay, on spontaneous motor activity (SMA) and wire hanging performance (WHP). Drug doses were administered 30 min before radiation exposure and neurobehavioral testings. The results showed a dose-dependent increase in radioprotection and an inhibition in the neuromotor tasks. The radioprotective efficacy was seen at doses at which intrinsic neuromotor deficits were detected (100-400 mg/kg). A dose-related parallelism of protective efficacy and neurobehavioral toxicity (i.e., SMA inhibition and WHP disruption) was also observed. The present findings suggest that WR-2721 induces neuromotor dysfunctions along with its radioprotectivity.