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J Dworkin

Publications and source records attributed to J Dworkin.

At least 19 recordsLinked to original sources
PubMed2001

Differential gene expression governed by chromosomal spatial asymmetry.

The activity of the transcription factor sigmaF is confined to one (the forespore) of two cells created by asymmetric division during sporulation in B. subtilis. We show that sigmaF activation is partly governed by the position of the gene for the unstable anti-sigmaF factor SpoIIAB. Because cytokinesis precedes chromosome segregation, most of the chromosome is translocated into the forespore after division. We hypothesize that because spoIIAB enters the forespore late, SpoIIAB lost to proteolysis is temporarily not replenished. Thus, chromosome asymmetry would be translated into the asymmetric distribution of SpoIIAB. Supporting this idea, transposition of spoIIAB to sites present in the forespore at the time of division impaired sporulation when a second pathway that participates in sigmaF activation was disabled.

Bacillus subtilis↗
PubMed2001

Self-assembling amphiphilic molecules: Synthesis in simulated interstellar/precometary ices.

Interstellar gas and dust constitute the primary material from which the solar system formed. Near the end of the hot early phase of star and planet formation, volatile, less refractory materials were transported into the inner solar system as comets and interplanetary dust particles. Once the inner planets had sufficiently cooled, late accretionary infall seeded them with complex organic compounds [Oró, J. (1961) Nature (London) 190, 389-390; Delsemme, A. H. (1984) Origins Life 14, 51-60; Anders, E. (1989) Nature (London) 342, 255-257; Chyba, C. F. & Sagan, C. (1992) Nature (London) 355, 125-131]. Delivery of such extraterrestrial compounds may have contributed to the organic inventory necessary for the origin of life. Interstellar ices, the building blocks of comets, tie up a large fraction of the biogenic elements available in molecular clouds. In our efforts to understand their synthesis, chemical composition, and physical properties, we report here that a complex mixture of molecules is produced by UV photolysis of realistic, interstellar ice analogs, and that some of the components have properties relevant to the origin of life, including the ability to self-assemble into vesicular structures.

Astronomy↗
PubMed2001

How urban African American young adolescents spend their time: time budgets for locations, activities, and companionship.

The time budgets of a population of youth provide important information about their daily experience and socialization. This study reports data on the time budgets of a sample of 253 urban African American poor to working- and middle-class 5th-8th graders in Chicago. These youth were found to spend less time in school than other postindustrial adolescent populations, but spent no less time doing homework than White suburban U.S. young adolescents. They spent large quantities of time at home and with their families--at rates comparable to rates for young adolescents in a society with collectivist values like India. Unlike with other populations, early adolescence was not associated with major age changes in time allocations. Amount of time in schoolwork did not differ by grade, and amount of time with family did not show the decline with age that has been found for European American suburban adolescents.

Adolescent↗
PubMed2001

Men's work and family lives in India: the daily organization of time and emotion.

This article examines daily patterns of work and family life for a sample of middle-class men in northern India. One hundred fathers of 8th graders provided information on their hour-to-hour time use and subjective states, by means of the experience sampling method. They reported little time spent on family work but substantial amounts of time with their children and thinking about their families. At their jobs, they reported high levels of attention but more negative emotion. By contrast, the home sphere elicited lower attention, more favorable affect, and more feeling of choice. Unlike for American samples, little relationship was found between experience at work and home, including little influence of men's work emotions on the family in the evening. These findings reflect how strong traditional family roles in India shape men's daily lives.

Adult↗
PubMed2000

Roles of the surface layer proteins of Campylobacter fetus subsp. fetus in ovine abortion.

The role of the surface (S)-layer proteins of Campylobacter fetus subsp. fetus has been investigated using an ovine model of abortion. Wild-type strain 23D induced abortion in up to 90% of pregnant ewes challenged subcutaneously. Isolates recovered from both dams and fetuses expressed S-layer proteins with variable molecular masses. The spontaneous S-layer-negative variant, strain 23B, neither colonized nor caused abortions in pregnant ewes. A series of isogenic sapA and recA mutants, derived from 23D, also were investigated in this model. A mutant (501 [sapA recA(+)]) caused abortion in one of five challenged animals and was recovered from the placenta of a second animal. Another mutant (502 [sapA recA]) with no S-layer protein expression caused no colonization or abortions in challenged animals but caused abortion when administered intraplacentally. Mutants 600(2) and 600(4), both recA, had fixed expression of 97- and 127-kDa S-layer proteins, respectively. Two of the six animals challenged with mutant 600(4) were colonized, but there were no abortions. As expected, all five strains recovered expressed a 127-kDa S-layer protein. In contrast, mutant 600(2) was recovered from the placentas of all five challenged animals and caused abortion in two. Unexpectedly, one of the 16 isolates expressed a 127-kDa rather than a 97-kDa S-layer protein. Thus, these studies indicate that S-layer proteins appear essential for colonization and/or translocation to the placenta but are not required to mediate fetal injury and that S-layer variation may occur in a recA strain.

Abortion, Veterinary↗
PubMed2000

The PspA protein of Escherichia coli is a negative regulator of sigma(54)-dependent transcription.

In Eubacteria, expression of genes transcribed by an RNA polymerase holoenzyme containing the alternate sigma factor sigma(54) is positively regulated by proteins belonging to the family of enhancer-binding proteins (EBPs). These proteins bind to upstream activation sequences and are required for the initiation of transcription at the sigma(54)-dependent promoters. They are typically inactive until modified in their N-terminal regulatory domain either by specific phosphorylation or by the binding of a small effector molecule. EBPs lacking this domain, such as the PspF activator of the sigma(54)-dependent pspA promoter, are constitutively active. We describe here the in vivo and in vitro properties of the PspA protein of Escherichia coli, which negatively regulates expression of the pspA promoter without binding DNA directly.

Bacterial Proteins↗
PubMed1998

A protein-induced DNA bend increases the specificity of a prokaryotic enhancer-binding protein.

Control of transcription in prokaryotes often involves direct contact of regulatory proteins with RNA polymerase from binding sites located adjacent to the target promoter. Alternatively, in the case of genes transcribed by Escherichia coli RNA polymerase holoenzyme containing the alternate sigma factor sigma54, regulatory proteins bound at more distally located enhancer sites can activate transcription via DNA looping by taking advantage of the increasing flexibility of DNA over longer distances. While this second mechanism offers a greater possible flexibility in the location of these binding sites, it is not clear how the specificity offered by the proximity of the regulatory protein and the polymerase intrinsic to the first mechanism is maintained. Here we demonstrate that integration host factor (IHF), a protein that induces a sharp bend in DNA, acts both to inhibit DNA-looping-dependent transcriptional activation by an inappropriate enhancer-binding protein and to facilitate similar activation by an appropriate enhancer-binding protein. These opposite effects have the consequence of increasing the specificity of activation of a promoter that is susceptible to regulation by proteins bound to a distal site.

Bacterial Proteins↗
PubMed1997

Role of upstream activation sequences and integration host factor in transcriptional activation by the constitutively active prokaryotic enhancer-binding protein PspF.

PspF, the transcriptional activator of the pspA operon of Escherichia coli, which belongs to the enhancer binding protein (EBP) family of sigma54 activator proteins, is constitutively active in an in vitro transcription assay. PspF protein, together with RNA polymerase holoenzyme containing sigma54, is required for in vitro transcription from the pspA promoter. EBP proteins are typically subject to regulation either by post-translational modification or interaction of a specific ligand with an N-terminal regulatory domain. However, unlike other members of the EBP family, PspF lacks this domain. pspA is positively regulated by IHF in vitro, and this regulation is dependent on the topology of the DNA; a linear template is much more dependent on IHF than a supercoiled template. EBP binding to upstream activating sequences (UAS) in their target promoters is mediated by the C-terminal domain which contains a helix-turn-helix DNA-binding motif. A mutant PspF protein lacking the C-terminal DNA-binding domain is active in vitro, although at much higher concentrations than the wild-type protein. In vitro transcription from pspA templates missing one or both of the UAS sites is reduced relative to wild-type templates, but is still appreciable; however, IHF acts as a negative regulator of pspA transcription on these mutant templates. Thus, PspF bound to non-specific sequences upstream of the pspA promoter can activate pspA transcription, but this activation is inhibited by IHF. These data, taken together, support the model that a precise promoter geometry is necessary for IHF to positively regulate transcription and that IHF may act to prevent activation from inappropriately spaced upstream sites.

Bacterial Proteins↗
PubMed1997

Nested DNA inversion as a paradigm of programmed gene rearrangement.

Programmed gene rearrangements are employed by a variety of microorganisms, including viruses, prokaryotes, and simple eukaryotes, to control gene expression. In most instances in which organisms mediate host evasion by large families of homologous gene cassettes, the mechanism of variation is not thought to involve DNA inversion. Here we report that Campylobacter fetus, a pathogenic Gram-negative bacterium, reassorts a single promoter, controlling surface-layer protein expression, and one or more complete ORFs strictly by DNA inversion. Rearrangements were independent of the distance between sites of inversion. These rearrangements permit variation in protein expression from the large surface-layer protein gene family and suggest an expanding paradigm of programmed DNA rearrangements among microorganisms.

Bacterial Outer Membrane Proteins↗
PubMed1997

Objective evaluation of the quality of voice following radiation therapy for T1 glottic cancer.

BACKGROUND: Radiation therapy is commonly considered the treatment of choice for T1 glottic cancer. While it is generally believed that the quality of voice following irradiation is quite satisfactory, few studies have reported the results of objective assessment of voice after radiation therapy. PURPOSE: To objectively evaluate the quality of voice following radiation therapy for T1 glottic cancer. MATERIALS AND METHODS: The voices of 12 patients treated for T1 glottic cancer with radiation therapy were evaluated by acoustic analysis and speech aerodynamic studies. Eleven patients received between 6300 and 6665 cGy at a daily fraction size of 180-225 cGy. One patient received 7000 cGy at a daily fraction size of 200 cGy. Evaluation of the quality of voice was done 3 months to 7 years following completion of radiation therapy. RESULTS: The number of patients who scored abnormal values for the measurements of fundamental frequency, jitter, shimmer and harmonic to noise ratio was 2, 10, 4 and 3, respectively. The number of patients who scored abnormal values for transglottic airflow rate, subglottal pressure and glottal resistance was 12, 8 and 9, respectively. None of the studied patients scored normal values in all given tests. CONCLUSION: Although radiation therapy cures a high proportion of patients with T1 glottic cancer, the quality of voice does not return to normal following treatment.

Acoustics↗
PubMed1997

The Escherichia coli phage-shock-protein (psp) operon.

The phage-shock-protein (psp) operon helps to ensure survival of Escherichia coli in late stationary phase at alkaline pH, and protects the cell against dissipation of its proton-motive force against challenge. It is strongly induced by filamentous phage pIV and its bacterial homologues, and by mutant porins that don't localize properly, as well as by a number of other stresses. Transcription of the operon is dependent on sigma54 and a constitutively active, autogenously controlled activator. psp-operon expression is controlled by one negatively and several positively acting regulators, none of which is a DNA-binding protein. The major product of the operon, PspA, may also serve as a negative regulator of an unusual porin, OmpG.

Escherichia coli↗
PubMed1997

Molecular mechanisms of Campylobacter fetus surface layer protein expression.

Cells of the Gram-negative bacteria Campylobacter fetus are covered by monomolecular arrays of surface layer proteins (SLPs) critical for both persistence in their natural hosts and for virulence. For C. fetus cells, expression of SLPs essentially eliminates C3b binding and their antigenic variation thwarts host immunological defences. Each cell possesses multiple partially homologous and highly conserved SLP gene cassettes, tightly clustered in the genome, that encode SLPs of 97-149 kDa. These attach non-covalently via a conserved N-terminus to the cell wall lipopolysaccharide. Recent studies indicate that C. fetus reassorts a single promoter, controlling SLP expression, and one, or more, complete open reading frame strictly by DNA inversion, and that rearrangement is independent of the distance between sites of inversion. In contrast to previously reported programmed DNA inversion systems, inversion in C. fetus is recA-dependent. These rearrangements permit variation in protein expression from the family of SLP genes and suggest an expanding paradigm of programmed DNA rearrangements among microorganisms.

Animals↗
PubMed1997

Social workers and national health care: are there lessons from Great Britain?

This article reviews the experience of British social workers with the National Health Service (NHS) to inform American social workers as they advocate for changes in the U.S. health care system. The study focuses on the creation of the NHS in 1948, the development of local social services departments in 1968, and the full implementation of community care in 1993. Of particular interest are the British view of health care as a social service, the close relationship between the NHS and local social services, the relationship between social workers and physicians, and the impact of care management on social work. Although the current American political environment is not receptive to a social orientation to health care, a bold policy position grounded in a social context will provide a vision for the future.

Community Health Services↗
PubMed1997

Autogenous control of PspF, a constitutively active enhancer-binding protein of Escherichia coli.

Escherichia coli sigma54-dependent phage shock protein operon (pspA to -E) transcription is under the control of PspF, a constitutively active activator. Sigma70-dependent transcription of pspF is under autogenous control by wild-type PspF but not by a DNA-binding mutant, PspF deltaHTH. Negative autoregulation of PspF is continual and not affected by stimuli, like f1 pIV, that induce the pspA to -E operon. PspF production is independent of PspA (the negative regulator of the pspA to -E operon) and of PspB and -C (positive regulators).

Bacterial Proteins↗
PubMed1997

Nested DNA inversion of Campylobacter fetus S-layer genes is recA dependent.

Wild-type strains of Campylobacter fetus are covered by a monomolecular array of surface layer proteins (SLPs) critical for virulence. Each cell possesses eight SLP gene cassettes, tightly clustered in the genome, that encode SLPs of 97 to 149 kDa. Variation of SLP expression occurs by a mechanism of nested DNA rearrangement that involves the inversion of a 6.2-kb sapA promoter-containing element alone or together with one or more flanking SLP gene cassettes. The presence of extensive regions of identity flanking the 5' and 3' ends of each SLP gene cassette and of a Chi-like recognition sequence within the 5' region of identity suggests that rearrangement of SLP gene cassettes may occur by a generalized (RecA-dependent) homologous recombination pathway. To explore this possibility, we cloned C. fetus recA and created mutant strains by marker rescue, in which recA is disrupted in either S+ or S- strains. These mutants then were assessed for their abilities to alter SLP expression either in the presence or absence of a complementary shuttle plasmid harboring native recA. In contrast to all previously reported programmed DNA inversion systems, inversion in C. fetus is recA dependent.

Bacterial Outer Membrane Proteins↗
PubMed1996

Generation of Campylobacter fetus S-layer protein diversity utilizes a single promoter on an invertible DNA segment.

Wild-type strains of Campylobacter fetus contain a monomolecular array of surface layer proteins (SLPs) and vary the antigenicity of the predominant SLP expressed. Reciprocal recombination events among the eight genomic SLP gene cassettes, which encode 97- to 149 kDa SLPs, permit this variation. To explore whether SLP expression utilizes a single promoter, we created mutant bacterial strains using insertional mutagenesis by rescue of a marker from plasmids. Experimental analysis of the mutants created clearly indicates that SLP expression solely utilizes the single sapA promoter, and that for variation C. fetus uses a mechanism of DNA rearrangement involving inversion of a 6.2 kb segment of DNA containing this promoter. This DNA inversion positions the sapA promoter immediately upstream of one of two oppositely oriented SLP gene cassettes, leading to its expression. Additionally, a second mechanism of DNA rearrangement occurs to replace at least one of the two SLP gene cassettes bracketing the invertible element. As previously reported promoter inversions in prokaryotes, yeasts and viruses involve alternate expression of at most two structural genes, the ability of C. fetus to use this phenomenon to express one of multiple cassettes is novel.

Bacterial Outer Membrane Proteins↗