MKP-1 (3CH134), an immediate early gene product, is a dual specificity phosphatase that dephosphorylates MAP kinase in vivo

Mitogenic stimulation of cells induces rapid and transient activation of MAP kinases. Here we report that a growth factor-inducible gene, 3CH134, encodes a dual specificity phosphatase that dephosphorylates and inactivates p42MAPK both in vitro and in vivo. In vitro, 3CH134 protein dephosphorylates both T183 and Y185 in p42MAPK. In serum-stimulated normal fibroblasts, the kinetics of inactivation of p42MAPK coincides with the appearance of newly synthesized 3CH134 protein, and the protein synthesis inhibitor cycloheximide leads to persistent activation of MAP kinase. Expression of 3CH134 in COS cells leads to selective dephosphorylation of p42MAPK from the spectrum of phosphotyrosyl proteins. 3CH134 blocks phosphorylation and activation of p42MAPK mediated by serum, oncogenic Ras, or activated Raf, whereas the catalytically inactive mutant of the phosphatase, Cys-258-->Ser, augments MAP kinase phosphorylation under similar conditions. The mutant 3CH134 protein also forms a physical complex with the phosphorylated form of p42MAPK. These findings suggest that 3CH134 is a physiological MAP kinase phosphatase; we propose the name MKP-1 for this phosphatase.

The growth factor-inducible immediate-early gene 3CH134 encodes a protein-tyrosine-phosphatase

Stimulation of fibroblasts with serum growth factors results in the rapid activation of a set of immediate-early genes, among them 3CH134. We have purified a bacterially expressed form of the 3CH134-encoded polypeptide and demonstrated that it has intrinsic protein-tyrosine-phosphatase (PTPase; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48) activity in vitro. This activity is optimal at pH 7.5, is sensitive to vanadate and cysteinyl modifying agents, and is insensitive to a panel of serine/threonine phosphatase inhibitors. Purified 3CH134 protein displays a high degree of selectivity among the tyrosine-phosphorylated polypeptide substrates tested. Under our assay conditions, the rates of dephosphorylation are in the order EDNDYINASL peptide < myelin basic protein < reduced, carboxyamidomethylated, and maleylated lysozyme (RCML) < p42mapk. There is a 200-fold range in rates for these substrates, with p42mapk dephosphorylated 15-fold more rapidly than RCML. Although 3CH134 is most closely related to the tyrosine/serine dual-specificity phosphatase VH1, we failed to detect any 3CH134-directed activity on casein or RCML phosphorylated on serine/threonine residues by cAMP-dependent protein kinase. Since 3CH134 expression is controlled transcriptionally and posttranscriptionally, it may represent a class of PTPases whose activity is regulated at the level of protein synthesis and degradation.

Serum protein-binding characteristics of vancomycin

A synthesis of studies of serum protein binding of vancomycin and its reported abnormal binding in serum with very high concentrations of immunoglobulin A (IgA) suggests that this antibiotic may be bound to more than one serum protein. Using an ultrafiltration method for separating free from bound drug and high-performance liquid chromatography to measure drug concentration, we studied the binding characteristics of vancomycin for alpha-1 acid glycoprotein, IgG, IgM, IgA, and albumin. The results showed that vancomycin does not bind to alpha-1 acid glycoprotein, IgG, or IgM. Major binding to albumin and IgA occurs, and total drug binding to serum proteins can be fully explained by binding to these two proteins. We calculated an N (number of binding sites per molecule) of 1.3 +/- 0.4 and a K (association constant) of 3.3 x 10(5) +/- 6.3 x 10(4) M-1 (NK = 4.3 x 10(5) M-1) for binding to IgA, whereas the corresponding NK value for albumin was only 527.5 M-1, indicating that vancomycin preferentially binds to IgA. Very high concentrations of IgA in serum (i.e., grams per deciliter), such as in patients with IgA myeloma, may result in the paradox of high (total) concentrations of vancomycin in serum that may be clinically ineffective.

A protein-tyrosine/serine phosphatase encoded by the genome of the cyanobacterium Nostoc commune UTEX 584

Protein-tyrosine phosphorylation has long been regarded as an exclusively eukaryotic phenomenon. Although some non-eukaryotes, mainly viruses, possess genes encoding protein-tyrosine kinases or protein-tyrosine phosphatases, these were probably appropriated from the eukaryotic hosts that constitute the sites of action of these enzymes. Herein we identify a gene, iphP, from the chromosome of the cyanobacterium Nostoc commune UTEX 584 that contains the His-Cys-Xaa-Ala-Gly-Xaa-Xaa-Arg sequence characteristic of known protein-tyrosine phosphatases. The expressed gene product, IphP, displayed protein-tyrosine phosphatase activity toward phosphotyrosine residues on reduced, carboxyamidomethylated, and maleylated lysozyme with optimum activity at pH 5.0. In addition, IphP dephosphorylated the phosphoseryl groups on casein that had been phosphorylated by the cAMP-dependent protein kinase. Cell lysates of N. commune probed with antibodies to phosphotyrosine indicated the presence of a tyrosine-phosphorylated protein of M(r) approximately 85 kDa. This tyrosine-phosphorylated protein was detected in cells grown in the presence of combined nitrogen but not in nitrogen-deficient media that induces the formation of differentiated N2-fixing cells (heterocysts). Together, these data suggest a role for protein-tyrosine phosphorylation in regulating cellular functions in this cyanobacterium. IphP is the first protein-tyrosine phosphatase to be discovered that is encoded by the chromosomal DNA of any prokaryote. Given the free-living nature of N. commune and the phylogenetic antiquity of the cyanobacteria, these findings suggest for the first time the existence of a protein-tyrosine phosphatase of genuine, unambiguous prokaryotic ancestry, thus raising fundamental questions as to the origin and role of tyrosine phosphorylation.

[Ureaplasma urealyticum and intrauterine infection of fetus]

Ureaplasma urealyticum (Uu) infection in pregnancy can lead to a poor outcome. To confirm the relation between Uu and intrauterine infection, 65 placentas were taken for isolation and identification of Uu from pregnant women with positive antibody to Uu. Uu was isolated from 13 (20%) of the 65 placentas. The pathologic examination of 6 placentas showed that there were acute or chronic inflammatory cell infiltration. Cord blood IgM antibody was examined by ELISA from 5 cases in which Uu was isolated from placentas and 3 of them was positive to Uu. The 5 cord blood specimens were assayed by the metabolic inhibition test for serotypes of Uu, and one of them was serotype 8. Since the isolation of Uu from some pregnant women, the pathologic changes of placentas, and the detection of specific IgM from cord blood showed a good consistency, we conclude that the Uu infection may occur in utero.

Atrial natriuretic peptide inhibits growth of hepatoblastoma (HEP G2) cells by means of activation of clearance receptors

To investigate whether atrial natriuretic factor regulates the growth of hepatocytes and to determine the receptor subtype involved in such modulation, we studied the effect of atrial natriuretic factor 103-126 and clearance receptor binding analogs of atrial natriuretic factor, (des-(Q116, S117, G118, L119, G120) atrial natriuretic factor 102-121 and des-(C105,121) atrial natriuretic factor 104-126) on growth of human hepatoblastoma cells. Atrial natriuretic factor 103-126 and des-(Q116, S117, G118, L119, G120) atrial natriuretic factor 102-121 inhibited thymidine incorporation into human hepatoblastoma cells cultured in the presence of bovine serum albumin and epidermal growth factor but not in cells cultured in bovine serum albumin alone. Moreover, atrial natriuretic factor 103-126, des-(Q116, S117, G118, L119, G120) atrial natriuretic factor 102-121 and des-(C105,121) atrial natriuretic factor 104-126, in a concentration-dependent manner, inhibited thymidine incorporation and cell proliferation. As monitored by the ability of des-(Q116, S117, G118, L119, G120) atrial natriuretic factor 102-121 to displace 125I-labeled atrial natriuretic factor, epidermal growth factor increased the expression of cell surface clearance receptors. Epidermal growth factor also transiently increased the cellular content of atrial natriuretic factor clearance receptor messenger RNA without altering the levels of guanylyl cyclase-linked atrial natriuretic factor receptor messenger RNA levels. Maximal increase in atrial natriuretic factor clearance receptor messenger RNA coincided with the maximal increase in des-(Q116, S117, G118, L119, G120) atrial natriuretic factor 102-121-displaceable 125I-atrial natriuretic factor binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of poor control of film processors on mammographic image quality

With the increasingly stringent standards of image quality in mammography, film processor quality control is especially important. Current methods are not sufficient for ensuring good processing. The authors used a sensitometer and densitometer system to evaluate the performance of 22 processors at 16 mammographic facilities. Standard sensitometric values of two films were established, and processor performance was assessed for variations from these standards. Developer chemistry of each processor was analyzed and correlated with its sensitometric values. Ten processors were retested, and nine were found to be out of calibration. The developer components of hydroquinone, sulfites, bromide, and alkalinity varied the most, and low concentrations of hydroquinone were associated with lower average gradients at two facilities. Use of the sensitometer and densitometer system helps identify out-of-calibration processors, but further study is needed to correlate sensitometric values with developer component values. The authors believe that present quality control would be improved if sensitometric or other tests could be used to identify developer components that are out of calibration.

Simplification of antibiotic dose adjustments in renal insufficiency: the DREM system

Many clinicians, unassisted by reference books, are unable to make the required dose adjustment of antibiotics needed when a patient has renal insufficiency. We describe the DREM (dosing in renopathy by easy-to-use multipliers) system, which simplifies the understanding and the process of dose adjustment. DREM is a two-step process: Cockcroft and Gault estimation of creatinine clearance (CLcr) from age, sex, and serum creatinine and calculation of the adjusted dose or dosing interval by multipliers. If the normal dose is multiplied by the dose multiplier (CLcr/100) and the dosing interval by the interval multiplier (100/CLcr), the adjusted dose and interval, respectively, are obtained. Theoretical trough concentrations calculated with the DREM system correlated closely (r = 0.9) with actual concentrations obtained from doses calculated by the Hull and Sarubbi method in 23 patients. With DREM, gentamicin or tobramycin trough concentrations above 2 micrograms/ml were less likely to occur. The DREM system is a simple and easily remembered method for dose adjustments of certain anti-infective agents in renal insufficiency. Dose estimates with this method are reasonably accurate and compare favourably with other standard methods of correction.

Stability analysis for grating-tuned strong-external-feedback semiconductor lasers

We give a simple stability analysis within the scope of steady-state solution for the grating-tuned strong-external-feedback semiconductor lasers. In our model, a fluctuation in the refractive index of an active medium through the coupling of carrier density will cause another fluctuation in the refractive index. If the latter is always smaller than the former, the fluctuation will be damped, and therefore the corresponding operating point of the laser is stable. Our analysis indicates that there are various stable and unstable operating-frequency ranges for various reflectivities of the internal facet of the laser diode. In addition, it agrees well with the experimental results and explains the bistability of threshold gain versus operating frequency.

Analysis of polarization dynamics by singularity decomposition method

The driving point immittance (impedance or admittance) function is commonly used in electrical characterization of polarized materials and interfaces. The immittance function typically attenuates following a power function dependence on frequency. This fact has been recognized as a macroscopic dynamical property manifested by strongly interacting dielectric, viscoelastic and magnetic materials and interfaces between different conducting substances. Linear interfacial polarization processes which occur at metal electrode-electrolyte interfaces have been represented by the Fractional Power Pole [FPP] function in single or multiple stages. The FPP function is referred to as the Davidson-Cole function in the dielectrics literature. A related function widely used in mathematical modeling of dielectric and viscoelastic polarization dynamics is the Cole-Cole function. The fractional power factor which parametrizes the FPP or the Davidson-Cole function has been shown earlier to equal the logarithmic ratio of the locations of the pole-zero singularities. In this paper we first review a modified form of the singularity decomposition of the FPP function accomplished within a prescribed error range. The distribution spectrum and the corresponding simulation by a cascade R-C network, as opposed to the synthesis by a ladder R-C network, are readily obtained as the next step in the simulation. The method is then applied to decompose the Cole-Cole function; the pole-zero placement of the singularity function is determined and the equivalent cascade R-C network is synthesized.

[Effects of McAbs HIP2, APT4 and HI117 on the human platelet cytoskeleton]

The effects of monoclonal antibodies HIP2, APT4 and HI117 on the platelet cytoskeleton were investigated. The results showed that HIP2, APT4 and HI117 could induce an increase of platelet cytoskeleton materials in PRP. The action of HIP2 and APT4 could be obviously inhibited by the calmodulin inhibitor EBB. The inhibition rates of EBB were 76.3% and 48.95%, respectively. But EBB couldn't inhibit the HI117-induced an increase of platelet cytoskeleton materials. EBB could completely inhibit APT4-induced platelet aggregation(100%) and partially inhibit HIP2-induced platelet aggregation (14.26%). It couldn't inhibit HI117-induced platelet aggregation. These McAbs couldn't induce aggregation and actin mobilization in washed platelets in the presence of EDTA. The results indicate that platelet aggregation and the increase of actin induced by these McAbs, in addition to Ca2+, could be related to a factor or factors in the plasma. The Ca(2+)-CM system might play an important role in platelet aggregation and actin mobilization induced by HIP2 and APT4.

Genetic and physical analyses of sister chromatid exchange in yeast meiosis

We have used nonessential circular minichromosomes to monitor sister chromatid exchange during yeast meiosis. Genetic analysis shows that a 64-kb circular minichromosome undergoes sister chromatid exchange during 40% of meioses. This frequency is not reduced by the presence of a homologous linear minichromosome. Furthermore, sister chromatid exchange can be stimulated by the presence of a 12-kb ARG4 DNA fragment, which contains initiation sites for meiotic gene conversion. Using physical analysis, we have directly identified a product of sister chromatid exchange: a head-to-tail dimer form of a circular minichromosome. This dimer form is absent in a rad50S mutant strain, which is deficient in processing of the ends of meiosis-specific double-stranded breaks into single-stranded DNA tails. Our studies suggest that meiotic sister chromatid exchange is stimulated by the same mechanism as meiotic homolog exchange.

Stereoselective degradation of the fenoprofen acyl glucuronide enantiomers and irreversible binding to plasma protein

Stereoselective degradation of fenoprofen (FEN) glucuronides and irreversible binding of FEN enantiomers to human serum albumin via their glucuronides were studied. At different pH values, 37 degrees C, and in the absence of albumin, degradation half-lives were diastereomeric, resulting mainly from a combination of hydrolysis and acyl migration. Lower pH enhanced FEN glucuronide stability and reduced the extent of irreversible binding. The degradation rate of R-FEN glucuronide was greater than that of the S-glucuronide (S-FEN). When human serum albumin was added to the medium, stability was decreased as compared to protein-free buffer. FEN glucuronides were readily hydrolyzed to parent drug, indicating an esterase-like activity of the albumin molecule. In vitro irreversible binding was higher for R-FEN (1.22% +/- 0.36) than for S-FEN glucuronide (0.76% +/- 0.12), when a 0.1 mM concentration of each conjugate enantiomer was incubated under physiological conditions (pH 7.4, 37 degrees C). Incubation with unconjugated FEN did not lead to measurable irreversible binding. Analysis of plasma samples from a clinical study showed that enantioselective irreversible binding of FEN to plasma proteins also occurs in vivo. After administration of a single 600-mg dose of racemic FEN to six healthy volunteers, covalent binding of R- and S-FEN to plasma proteins was measured in all subjects. The percentage of S-FEN protein adduct was greater than that of its R-enantiomer adduct. Total amounts of FEN irreversibly bound to plasma protein in vivo were also very low (1.02 +/- 0.32 and 3.23 +/- 0.85 mol/mol protein x 10(-4) for R- and S-FEN, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of ceftriaxone binding to immunoglobulin G and potential clinical significance

The interaction between immunoglobulin G (IgG) and ceftriaxone was studied. Using an ultrafiltration method, we performed dose ranging studies at a ceftriaxone concentration range of 1 to 720 micrograms/ml in the presence of various concentrations of human IgG, human serum albumin (HSA), and combinations of IgG and HSA at pH 7.4 and 37 degrees C. The results showed that ceftriaxone binding to IgG was nonlinear and was consistent with the presence of two binding sites that possess different binding capacities and affinities. Except for increased peak percent binding as the IgG concentration increased, the binding characteristics did not change with IgG concentration. Binding to HSA was consistent, with the presence of only one high-affinity binding site. A mathematical model based on the observed data was constructed; this model was used to predict protein binding at various concentrations of drug, IgG, HSA, or combinations of IgG and HSA in buffer and in plasma medium. Correlations between the observed versus the predicted values were excellent in both media. Simulations with the model indicated that patients with hypergammaglobulinemia have an increased potential of being exposed to prolonged subinhibitory concentrations of ceftriaxone if the drug is given once every 24 h.

Extensive 3'-overhanging, single-stranded DNA associated with the meiosis-specific double-strand breaks at the ARG4 recombination initiation site

Meiosis-specific double-strand breaks occur at the initiation site for meiotic gene conversion in the yeast ARG4 gene. Here we show that the break fragments end in extensive 3'-overhanging, single-stranded tails. The single-stranded tails very in length, generating a gradient of single-strandedness that parallels the gradient of gene conversion frequencies in ARG4. In strains carrying a rad50S mutation, which blocks meiotic recombination, the extensive single-stranded tails do not form, suggesting that their generation is an obligatory step in meiotic recombination. Using the rad50S mutant, we have mapped the site of the ARG4 break to a small region within the genetically defined recombination initiation site. These results strongly support the double-strand break model of meiotic recombination.

Early events in liver allograft rejection. Delineation of sites of simultaneous intragraft and recipient lymphoid tissue sensitization

The early events of liver allograft rejection in untreated rats were studied in the DA to BN rejection strain combination and compared with DA and BN liver isograft recipients. In the liver allografts, T-cell infiltration first occurred at 2 days after transplantation and localized to the portal triads and subjacent to the terminal hepatic venules (THV), regions rich in intensely Ia + spindle and dendritic-shaped interstitial cells. Double staining showed distinct 'clustering' between donor Ia-positive dendritic-shaped cells and W3/25+ infiltrating lymphocytes, or to a lesser extent, OX8+ cells. The infiltrating mononuclear cells underwent blastogenesis and proliferated in both the triads and THV regions at 3 and 4 days. Donor Ia-positive cells were also noted in the W3/25+ periarterial lymphatic sheath and marginal zone of the recipient spleen 1 day after transplantation. The number of these cells in the spleen peaked at 3 to 4 days, but were no longer detectable by 10 to 12 days. Mitotic activity became evident in these same regions by days 3 and 4. Paracortical blastogenesis (day 2) and proliferation (days 3 and 4) were also noted in the regional lymph nodes of liver allograft recipients, but no donor Ia+ cells were found in the mesenteric nodes or thymus of the allograft recipients. These results demonstrate that sensitization of the recipient lymphoid tissue to liver allografts can occur both peripherally (intragraft) and centrally (spleen and lymph nodes). Passenger leukocytes (donor dendritic cells) are likely the primary stimulators of the rejection reaction. Still, it is probable that other pathways of sensitization exist.

Stereoselective analysis of fenoprofen and its metabolites

Reversed-phase high-performance liquid chromatographic assays have been developed to quantitate simultaneously fenoprofen and its major metabolites as well as to distinguish between their R- and S- enantiomers following a single oral dose of 600 mg racemic fenoprofen to healthy volunteers. The compounds are extracted from plasma (after precipitation of plasma protein) or assayed directly in diluted urine samples employing a gradient solution on a C18 column and ultraviolet detection. Two internal standards, ketoprofen and flunoxaprofen, are used to allow measurement of very low (0.05 microgram/ml) and high (70 microgram/ml) concentrations in each sample. R- and S-fenoprofen glucuronides can be separated directly; the 4'-hydroxyfenoprofen conjugates are measured via an indirect method by comparing the concentration of 4'-hydroxyfenoprofen before and after hydrolysis. The R- and S-enantiomers of both parent and 4'-hydroxy metabolite are derivatized with L-leucinamide via an ethyl chloroformate intermediate and subsequently analyzed on a C18 column. Concentrations of metabolites found in plasma were low when compared to parent drug. The S/R ratio of fenoprofen in plasma always exceeds 1 and increases with time after dosage while the S/R ratio of its 4'-hydroxy metabolite remains almost unchanged at 1.1. R-Fenoprofen glucuronide disappears rapidly from plasma as compared to its S-antipode; a less pronounced difference is noted between R- and S-4'-hydroxyfenoprofen conjugates. Fenoprofen is almost completely excreted as its S-acyl glucuronides; the renal clearance of unchanged drug is very low.

Pattern formation in an immobilized bienzyme system. A morphogenetic model

Experimental and theoretical studies of a reaction-diffusion model of two immobilized enzymes participating in the cellular acid-base metabolism, namely glutaminase and urease, are presented. The system shows an unstable steady state at pH 6.0, where any perturbation will drive the system towards a more alkaline or more acidic pH, owing to the autocatalytic behaviour with respect to pH exhibited by both enzymes. When diffusion is coupled to reaction by means of immobilization, different patterns of the internal pH profile appear across the membrane. If the bienzymic membrane is subjected to a perturbation at its boundaries, of the same amplitude but in opposite directions, the internal pH evolves through an asymmetric pattern to attain a nearly symmetric distribution of pH. The pH value at the final steady state is more acidic or more alkaline than the initial state according to the initial and boundary conditions. The final nearly symmetric state is attained more rapidly when less enzyme is immobilized (1.8 x 10(-4) M.s-1 as against 3.3 x 10(-4) M.s-1 of total enzyme activity in the membrane volume). The experimental results agree rather well qualitatively with numerical predictions of the model equations.

Tomography for reconstructing continuous fields from ill-posed multidirectional interferometric data

A computational tomographic technique has been developed to accurately reconstruct continuous flow fields of a simple shape from severely limited interferometric data. The algorithm is based on iterative reconstruction of the complementary field, the difference between the field to be reconstructed and its estimate. Its advantages lie in the treatment of various ill-posed problems in a unified manner and ease of incorporation of a priori information, even an approximate field shape. In principle it can utilize only available data. Test results demonstrated stable convergence and potential for substantial error reduction with a proper field estimate.

Clinical application of autogenous mandibular bone grafts. Analysis of 166 cases

Of the 166 patients receiving autogenous mandibular bone grafts during 1972-1987, 55 were used for repair of mandibular bone defect, 67 for correction of maxillofacial malformation and 44 for reconstruction of temporo-mandibular joint. Follow-up showed that 155 patients had satisfactory results after operation.

Genetic analysis of olfactory behavior in Drosophila: a new screen yields the ota mutants

A simple means of measuring Drosophila olfactory response is described, and the behavior which it measures is characterized. The assay was used to screen for X-linked mutants defective in olfactory function. Six ota mutants were isolated and characterized (ota = olfactory trap abnormal). Four of the mutants were found to be abnormal in another chemosensory behavior as well. Two of the mutant phenotypes extend to include another sensory system: they are defective in visual system physiology. All were normal, however, in a test of giant fiber system physiology. Two of the mutations are dominant, and the recessive mutations define two complementation groups. Mutations representing each complementation group, as well as one of the dominant mutations, were mapped. For the mutants with defective visual system physiology, the visual defects were shown to cosegregate with olfactory phenotypes.

Effects of atmospheric turbulence on photodetector arrays

In this paper we study quantitatively the effects of atmospheric turbulence on the measurement sensitivity of a quadrant detecting array, along with the measurement variance induced by atmospheric turbulence. Our results show that the stronger the turbulence strength, the lower the measurement sensitivity, and the larger the measurement variance. This agrees with the experimental phenomena we have observed up to now. In addition, the measurement sensitivity in the X direction could be affected by the deviation of light spots in the Y direction due to the existence of gaps between the quadrant elements. Such effects still exist for the measurement variance even when there are no gaps at all. This effect is analyzed quantitatively.

[24-hour ambulatory blood pressure monitoring in normal and hypertensive subjects]

24-hour ambulatory blood pressures (BP) of 172 normal subjects and 167 hypertensive patients recorded by automatic ambulatory monitoring device (A method) and standard mercury sphygmomanometer (B method) were studied. The results show: (1) 66% of normal subjects and 78% hypertensive patients have an evident circadian rhythm BP during 24-hours, BP readings during sleep and noon time are lower. (2) There is no significant difference between times at work and at home readings (P greater than 0.05), but the mean BP during sleeping time is the lowest (P less than 0.01). (3) The correlative coefficient of 24-hour average BP and casual clinic BP is low (r = 0.38-0.74). (4) The validity and accuracy of ambulatory BP monitoring by A and B methods were compared.

Interferometric tomography of continuous fields with incomplete projections

Interferometric tomography in the presence of an opaque object has been investigated. In principle the developed iterative algorithm does not need to augment the missing information. It is based on the successive reconstruction of the difference field, the difference between the object field to be reconstructed and its estimate, in the defined region only. The application of the algorithm results in stable convergence.

Double-strand breaks at an initiation site for meiotic gene conversion

It has been proposed that the initiation of meiotic recombination involves either single-strand or double-strand breaks in DNA. It is difficult to distinguish between these on the basis of genetic evidence because they give rise to similar predictions. All models invoke initiation at specific sites to explain polarity, which is a gradient in gene conversion frequency from one end of a gene to the other. In the accompanying paper we describe the localization of an initiation site for gene conversion to the promoter region of the ARG4 gene of the yeast Saccharomyces cerevisiae. Here, we show that a double-strand break appears at the ARG4 recombination initiation site at the time of recombination, and that the broken DNA molecules end in long single-stranded tails.

Characterization of the larval olfactory response in Drosophila and its genetic basis

Drosophila larvae are attracted to a wide variety of chemical stimuli. The olfactory response to ethyl acetate, a powerful attractant, was found to be surprisingly well conserved across a variety of different wild-type strains. Strain differences are documented, however, both in attraction to ethyl acetate and in another chemosensory behavior: avoidance of an aversive stimulus. As a means of analyzing the extent of genetic heterogeneity within strains, one wild-type population, Canton-S, was screened for variant X chromosomes. An enrichment procedure was characterized and used to make the screening more efficient. Lines homozygous for individual X chromosomes were established, and all were found to exhibit a strong olfactory response, although evidence was found for variation among them. The olfactory response was found to be conserved through an extended period of larval development, including the final period during which larvae leave the culture medium in preparation for metamorphosis. The results are discussed in terms of the genetic basis of the response and the use of single-gene mutations as a means of dissecting olfactory system function.