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Biomedical subjects

L Katz

Publications and source records attributed to L Katz.

At least 19 recordsLinked to original sources
PubMed1992

Biosynthesis of the erythromycin macrolactone and a rational approach for producing hybrid macrolides.

The three eryA genes involved in the formation of the polyketide portion of the macrolide antibiotic erythromycin in Saccharopolyspora erythraea, appear to be organized in a single transcriptional unit on the basis of the results of gene disruption experiments. An insertion sequence-like element of lower G + C content separates eryAI from eryAII. The organization of the enzymatic domains present in the eryA-encoded multifunctional polypeptides, determined by computer-assisted analysis, is presented. This has enabled the determination of a putative dehydratase domain. A rational approach for producing novel macrolides by introducing selected changes in polyketide synthase genes is outlined. The isolation of a lactone intermediate resulting from an early synthesis step in macrolactone formation is also presented.

Amino Acid Sequence↗
PubMed1992

Organization of the enzymatic domains in the multifunctional polyketide synthase involved in erythromycin formation in Saccharopolyspora erythraea.

Localization of the enzymatic domains in the three multifunctional polypeptides from Saccharopolyspora erythraea involved in the formation of the polyketide portion of the macrolide antibiotic erythromycin was determined by computer-assisted analysis. Comparison of the six synthase units (SU) from the eryA genes with each other and with mono- and multifunctional fatty acid and polyketide synthases established the extent of each beta-ketoacyl acyl-carrier protein (ACP) synthase, acyltransferase, beta-ketoreductase, ACP, and thioesterase domain. The extent of the enoyl reductase (ER) domain was established by detecting similarity to other sequences in the database. A segment containing the putative dehydratase (DH) domain in EryAII, with a potential active-site histidine residue, was also found. The finding of conservation of a portion of the DH-ER interdomain region in the other five SU, which lack these two functions, suggests a possible evolutionary path for the generation of the six SU.

3-Oxoacyl-(Acyl-Carrier-Protein) Synthase↗
PubMed1992

High-level expression and purification of mature HIV-1 protease in Escherichia coli under control of the araBAD promoter.

A 1.3-kb segment of Escherichia coli DNA containing the regulatory gene, araC, and the promoter of the araBAD operon was amplified by the polymerase chain reaction (PCR) and cloned into pUC18, resulting in plasmid pKB130 that produced the alpha fragment of beta-galactosidase upon addition of L-arabinose (L-ara). A synthetic gene for human immunodeficiency virus (HIV)-1 preprotease was placed downstream of the ara-BAD promoter in pKB130 to create a translational fusion inducible by addition of L-ara. The fusion protein correctly autoprocessed in vivo to yield a mature 99-amino-acid HIV-1 protease, which was found predominantly in inclusion bodies. This material could be refolded to an active form, which was purified to homogeneity. A small fraction of the protease was expressed in vivo as a soluble active form, which allowed the monitoring of expression during fermentation by a rapid and simple whole cell assay employing an HIV-1 protease-specific fluorogenic substrate.

Amino Acid Sequence↗
PubMed1992

Coping ability, stress, productive load, and symptoms.

A study of 450 college students demonstrated (a) the importance of a distinction between self-produced and externally produced stressors, (b) the usefulness of a construct of productive load, and (c) stronger relations of the Constructive Thinking Inventory than of the Hardiness Questionnaire with productive load and with mental and physical symptoms. Because a major path through which coping ability influences symptoms is negative emotions, the widely recommended practice of partialing self-reported negative affect out of relations among coping, stress, and symptoms is often inappropriate. However, as total daily stressors (e.g., hassles) consist largely of self-produced stressors, it is highly confounded with coping ability, and it is therefore important to partial coping ability out of relations between total stressors and other variables.

Adaptation, Psychological↗
PubMed1992

Nursing caries in Head Start children, St. Thomas U.S. Virgin Islands: assessed by examiners with different dental backgrounds.

The purposes of this study were to determine the prevalence of nursing caries in 3- to 5-year-old Head Start (HS) children on St. Thomas, U.S. Virgin Islands and to assess the reliability of examiners with different dental backgrounds. A dentist, hygienist, and nondental HS personnel participated in a 1/2 day training session (lecture and workshop) and then independently conducted visual examinations for caries of the maxillary anterior teeth including nursing caries. Twenty-three HS personnel examined a total of 375 children; the dentist and hygienist examined a random sample of 74 and 73 children, respectively. Seventy-one children received all three independent examinations. Reliability was assessed by percent agreement, sensitivity, specificity, and kappa value. The dentist found 41% of the children had caries of the maxillary incisors, which included nursing caries. The percentage of children with nursing caries was 12%. There was strong-to-good diagnostic agreement between the dentist and hygienist. The HS personnel also found that 12% of the children had nursing caries, but the diagnostic agreement between the dentist and HS personnel was only good-to-fair.

Bottle Feeding↗
PubMed1991

Modular organization of genes required for complex polyketide biosynthesis.

In Saccharopolyspora erythraea, the genes that govern synthesis of the polyketide portion of the macrolide antibiotic erythromycin are organized in six repeated units that encode fatty acid synthase (FAS)-like activities. Each repeated unit is designated a module, and two modules are contained in a single open reading frame. A model for the synthesis of this complex polyketide is proposed, where each module encodes a functional synthase unit and each synthase unit participates specifically in one of the six FAS-like elongation steps required for formation of the polyketide. In addition, genetic organization and biochemical order of events appear to be colinear. Evidence for the model is provided by construction of a selected mutant and by isolation of a polyketide of predicted structure.

Amino Acid Sequence↗
PubMed1991

Site-specific recombination in Escherichia coli between the att sites of plasmid pSE211 from Saccharopolyspora erythraea.

pSE211 from Saccharopolyspora erythraea integrates site-specifically into the chromosome through conservative recombination between attP and attB, the plasmid and chromosomal attachment sites. Integration depends on the presence of int, an open reading frame (ORF) that lies adjacent to attP and encodes the putative integrase. Immediately upstream of int lies xis (formerly called orf2) which encodes a basic protein that is thought to exhibit DNA binding. xis and int were cloned in various combinations in pUC18 and expressed constitutively in Escherichia coli from the lac promoter. attP and attB were cloned in Streptomyces or E. coli plasmids containing kanamycin resistance (KmR) or chloramphenicol resistance (CmR) markers. Stable KmR CmR cointegrates formed by attP x attB or attP x attP recombination (integration) were obtained in E. coli hosts that expressed int. Co-integrates were not found in hosts expressing int + xis. Excision (intraplasmid att site recombination) was examined by constructing plasmids carrying attL and attR or two attP sites separating CmR from KmR and by following segregation of the markers in various hosts. Both attL x attR and attP x attP excision depended on both xis and int in E. coli. pSE211 att site integration and excision were not affected by a deletion in himA, the gene encoding a subunit of integration host factor.

Actinomycetales↗
PubMed1991

The processing of inflected words.

Is an inflected word identified by first decomposing it into stem plus suffix or, instead, is it recognized as a whole? Several lexical decision experiments studied the recognition of inflected words in English (a language with few inflections) and Serbo-Croatian (a heavily inflected language). If recognition depended on decomposition, preceding the inflection with a brief exposure of the stem (less than 100 ms) should have primed the lexical entry for the stem and, therefore, facilitated recognition of the whole inflected word that followed. It did not. It was also found that the speed of recognizing an inflected word was more strongly associated with the frequency of the whole inflected form than with the frequency of its stem. The results suggested that in word recognition, lexical contact is first made with the whole word form. Nevertheless, morphological decomposition may still occur in subsequent processing.

Attention↗
PubMed1991

Constructive thinking and coping with laboratory-induced stress.

In a laboratory stress test, poor constructive thinkers produced more negative affective and cognitive responses in all experimental periods and a greater increase in such responses in the stress period than did good constructive thinkers. The groups differed in physiological arousal in the recovery period but not in the stress period. Stressor-instigated negative thoughts and spontaneous negative thoughts produced different patterns of relations with variables measured in the laboratory and with symptoms reported in everyday life. Discriminating patterns of relations were found between measures of cognition and affect in the laboratory and self-reported emotional, physical, and behavioral symptoms in everyday life. The results help explain the relation between maladaptive automatic thinking, on the one hand, and elevated physiological arousal and emotional, physical, and behavioral symptoms, on the other.

Adaptation, Psychological↗
PubMed1991

Developmental phases of sleep and motor behaviour in a cat mother-infant system: a time-lapse video approach.

The evolution of sleep patterns in developing kittens was studied using time-lapse video technology and direct observation. The duration, frequency, and onset of the behavioural states and interactions of the cats were analyzed and then organized into phases that represent major changes in developmental structure during the first 6 weeks of kitten life. We have demonstrated that the kittens began exhibiting adult bi-cyclic sleep patterns on approximately Day 30 of development. During the 10-day period that preceded this consolidation of sleep pattern, REM sleep decreased by half, with a reciprocal increase in NREM sleep. These changes were coincident with an increase in kitten patterned motor behaviour and an increase in stimulation of the kittens by the mother during her bi-cyclic active periods.

Animals↗
PubMed1991

Experimental study of atlas injuries. I. Biomechanical analysis of their mechanisms and fracture patterns.

Understanding injury mechanisms is important for the prevention, diagnosis, and treatment of spinal injuries. Using 10 fresh cadaveric human spine specimens of occiput to C3, clinically similar injuries of the atlas (C1) were produced with high-speed (4.4 m/sec) axial compression. The traumatic event was biomechanically monitored. The resulting injuries were studied with radiography, computed tomography, and a multidirectional instability test. The average compressive failure force was 3,050 N for specimens impacted in neutral posture (n = 437) and 2,100 N for those in extended posture (n = 282). Corresponding values for the impulse were 34.9 Nsec (n = 8.3) and 17.6 Nsec (n = 1.8). Average instability for both groups, as measured by the neutral zone and range of motion, increased by 90% and 44%, respectively, in flexion-extension and 20% in lateral bending, but not in axial rotation. These findings confirm the clinical observations.

Biomechanical Phenomena↗
PubMed1991

Experimental study of atlas injuries. II. Relevance to clinical diagnosis and treatment.

Atlas injuries were produced in vitro and evaluated by radiographic examinations and anatomic studies from a clinical viewpoint. Ten cadaveric human upper cervical spine specimens were subjected to a high-speed axial impact. Injuries to the atlas consisted of six bursting fractures, two ruptures of the transverse ligament, one four-part fracture without a prominent bursting, and one posterior arch fracture. The major soft tissue injury involved the transverse ligament. There were five bony avulsions and three midsubstance tears. In this study, computed tomographic examinations clearly demonstrated the sites of fracture and bony avulsions of the transverse ligament. The best diagnostic tool for function of the transverse ligament was determined to be the atlantodental interval on flexion radiographs. Axial traction force reduced a bursting fracture of the atlas ring. The in vitro atlas injury model gives useful information for clinical diagnosis and treatment.

Biomechanical Phenomena↗
PubMed1991

5'-Alkyl-substituted analogs of 5'-methylthioadenosine as trypanocides.

5'-Deoxy-5'-(methylthio)adenosine (MTA) is a by-product of polyamine metabolism and is phosphoryolytically cleaved to adenine and 5-deoxy-5-(methylthio)ribose-1-phosphate (MTR-1-P) by MTA phosphorylase. In eukaryotes, adenine is subsequently salvaged and converted to nucleotides, while MTR-1-P is converted to methionine. We examined 5'-deoxy-5'-substituted analogs of MTA for trypanocidal activity in vitro and in vivo. 5'-Deoxy-5'-(hydroxyethyl)thioadenosine (HETA) and its 5'-bromo,5'-chloro and 5'-fluoro derivatives were cleaved by extracts of the African trypanosome Trypanosoma brucei brucei (Km for MTA, 11.5 microM; Km for HETA, 13.2 microM) in a phosphate-dependent reaction. HETA and the three halo analogs were 50% inhibitory to growth at 0.5 to 5.0 microM in vitro. Inhibition of growth was reversible by exogenous methionine and 2-keto-4-methylthiobutyric acid, an intermediate in methionine synthesis from MTR-1-P. HETA was selected for further study in vivo. When administered by miniosmotic pump (25 to 150 mg/kg/day for 7 days) to mice infected with T. brucei brucei, HETA effected 70 to 90% cure rates. Results of this study indicate that these analogs of MTA are converted to trypanocidal MTR-1-P analogs and that this approach deserves further consideration in the development of novel chemotherapy of trypanosomiasis.

Adenosine↗
PubMed1990

Cloning of genes involved in erythromycin biosynthesis from Saccharopolyspora erythraea using a novel actinomycete-Escherichia coli cosmid.

Two plasmids were constructed that replicate in Saccharopolyspora (Sac.) erythraea, Escherichia coli and Streptomyces (S.) lividans, and used for the cloning of a locus involved in the synthesis of the macrolide antibiotic erythromycin (Er). Plasmid pAL7002 contains the thiostrepton-resistance gene (tsr), a replicon-containing fragment from pJVI and pUC9. Plasmid pNJI contains the lambda cos site but is otherwise similar to pAL7002. A library of total DNA from Sac. erythraea was constructed in pNJI and probed in colony hybridizations with a DNA fragment containing ermE, the Sac. erythraea ErR-encoding gene. Plasmids obtained were subsequently introduced into EryA mutants of Sac. erythraea blocked in synthesis of Er (Ery-) and transformants were screened for restoration of Er production (Ery+). Several plasmids were found to convert two mutants to Ery+, but a third EryA strain could not be restored to Ery+ by any of the plasmids employed. A 5-kb segment, designated eryAI, responsible for restoring the Ery+ phenotype in the EryA strains, was identified and mapped in the segment 12 to 17 kb downstream from ermE. Gene disruption experiments indicated that the 5-kb length of eryAI is fully internal to an eryAI-containing transcript. In Southern blots it was shown that one of the EryA strains carried a small deletion in eryAI and that, in at least some of the transformants restored to Ery+, the deletion had been replaced by the wild-type eryAI allele.(ABSTRACT TRUNCATED AT 250 WORDS)

Actinomycetaceae↗
PubMed1990

Cancer in Jewish migrants to Israel.

Data on the incidence of 15 cancers in the Jewish population of Israel from the period 1961-1981 have been studied with emphasis on the risk of disease in relation to birthplace, calendar time, and duration of residence in Israel. The results show wide variations in incidence by birthplace, from less than 2-fold for pancreatic cancer to a 40-fold difference for oesophageal cancer in females; the reasons for these are often little understood. The potential importance of environmental agents in aetiology for different migrant groups is discussed in relation to the size and rapidity of changes in risk related to the duration of residence in Israel.

Africa, Northern↗
PubMed1990

Lung cancer in Israel, 1962-1982. II. Ethnic differences among Jews.

Lung cancer incidence rates among Jews in Israel are significantly lower than in most developed countries in the world. A more detailed analysis of the rates among different Jewish ethnic groups also showed low rates. While Jewish males born in Europe-America (EA) had an 11% increase in rates between 1962-66 and 1977-82, Jewish males from Asian-African (AA) origin had a 45% increase resulting in current higher rates among North African than among East European Jews (the two dominant ethnic groups in Israel). In Jewish females, rates have been relatively stable from 1972 to 1982 and were almost twice as high for females born in EA than females born in AA with less prominent differences between countries. While smoking patterns probably explain the increase in rates among Asian-African Jewish males, other possible risk factors as well as the overall smoking prevalence cannot explain the low incidence in the major ethnic Jewish groups. The possibility of differed susceptibility is raised.

Adult↗