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Biomedical subjects

J R Walker

Publications and source records attributed to J R Walker.

At least 199 records · Page 11Linked to original sources
PubMed1971

Bacterial cell division regulation: physiological effects of crystal violet on Escherichia coli lon + and lon - strains.

The Escherichia coli lon(-) mutants apparently are defective in the ability to recommence cell division after temporary periods of deoxyribonucleic acid (DNA) synthesis inhibition. They are also more susceptible to cell division inhibition by the basic dye, crystal violet (CV), than are lon(+) strains. In enriched broth, the lon(+) strain continued to grow and divide in the presence of CV, but lon(-) cell division was inhibited and filamentous growth resulted. In a supplemented minimal medium containing CV, lon(-) cell division was only temporarily inhibited. There was no detectable specific effect on DNA synthesis, although CV slowed the rate of mass increase in both media. Trichloroacetic acid-insoluble lipid synthesis was preferentially inhibited in both lon(+) and lon(-) strains. In CV-containing enriched broth, diaminopimelic acid incorporation into trichloroacetic acid-insoluble compounds occurred at a rate greater than the rate of mass increase in both lon(+) and lon(-) strains. In a CV-containing supplemented minimal medium, diaminopimelic acid was incorporated to a greater extent by lon(-) cells than by lon(+) cells.

Bacterial Proteins↗
PubMed1970

Defective excision repair of pyrimidine dimers in the ultraviolet-sensitive Escherichia coli ras- mutant.

The ras(-) mutant of Escherichia coli K-12 is sensitive to ultraviolet (UV) light but only slightly sensitive to X-irradiation (1.5-fold increase). Other phenotypic properties include normal recombination ability and normal host cell reactivation ability but an abnormally high frequency of UV-induced mutation. The response of the ras(-) mutant to UV has been studied biochemically. After low doses of UV, the ras(-) mutant degraded excessive amounts of deoxyribonucleic acid, and long delays in resumption of deoxyribonucleic acid synthesis occurred. Pyrimidine dimers were excised at the normal rate. Although the mutant had the capability of initiating repair replication, the process was not completed after the high UV dose required to allow detection of repair replication. The ras(-) mutant, after low UV doses, left three to four times as many single-strand breaks not rejoined as did the wild-type strain.

Centrifugation, Density Gradient↗
PubMed1969

Escherichia coli ras locus: its involvement in radiation repair.

There are several classes of Escherichia coli mutants defective in radiation repair. These include strains defective in pyrimidine dimer excision, in photoreactivation, in recombination, in repair of X-ray damage, and ultraviolet (UV)-conditional mutants which do not divide after UV. Another mutant (ras(-)) has been isolated. The ras(-) has increased UV sensitivity, but only slightly increased X-ray sensitivity (1.5-fold increase). Ability to effect genetic recombination, to reactivate irradiated bacteriophage T1, and to be photoreactivated is normal. UV-induced mutation frequency is greatly increased in the mutant. The ras(-) apparently lacks the ability to repair some UV damage in the bacterial cell but can repair UV damage to bacteriophage DNA. The ras locus is located between lac and purE on the chromosome map.

Coliphages↗
PubMed1968

Evidence for a relationship between deoxyribonucleic acid metabolism and septum formation in Escherichia coli.

Septum formation is a key step in bacterial division, but the mechanism which controls periodic septum formation is unknown. In an attempt to understand this mechanism, lon(-) mutants, in which septum formation is blocked by very doses of ultraviolet light (UV), were investigated. UV must act on some part of the apparatus of cytokinesis; thus, identification of the UV target would identify part of this apparatus. As likely possibilities, UV might damage the septum-forming site or it might damage deoxyribonucleic acid (DNA), since DNA replication is normally coordinated with septum formation. To distinguish between these possibilities, DNA was specifically sensitized by incorporating bromodeoxyuridine into lon(-) bacteria. These bacteria were strongly sensitized to longer wavelength UV (2,900 to 3,100 A) so that they failed to form septa, grew into filaments which lysed, and did not form colonies. Various control experiments supported the conclusion that UV inhibits septum formation as a result of alterations in DNA metabolism. A relationship thus exists between DNA metabolism and septum formation.

Bromodeoxyuridine↗
PubMed1967

Conditional mutations involving septum formation in Escherichia coli.

The lon(-) mutation is responsible for a defect in cell division of Escherichia coli lightly irradiated with ultraviolet light (UV). These lon(-) mutants can be isolated readily by a procedure described here. Physiological studies were performed with the objective of determining the role of the lon gene. Unirradiated lon(-) mutants grow normally, except that a correlation of this mutation with capsule formation has been noted previously. These two properties can be separated, however. After irradiation, lon(-) grows as long filaments because septum formation is prevented. The filaments eventually lyse. Mass increase and deoxyribonucleic acid and enzyme synthesis appear to proceed normally. Thus, the lesion produced by UV appears to be highly specific. In bacteria that carry both genes (merozygotes), lon(+) is dominant to lon(-). Septum formation is restored to irradiated lon(-) bacteria by introduction of lon(+) by conjugation. Also, normal growth can be restored by nutritional variations. It is concluded that lon(+) is able to nullify the effects of the UV lesion under conditions where lon(-) cannot. Possibly, capsule precursors that can accumulate in the latter are responsible for the difference because they interfere with repair of the UV lesion.

Bacteriolysis↗
PubMed1966

Inoculum-dependent division lag of Bacillus cultures and its relation to an endogenous factor(s) ("schizokinen").

Lankford, C. E. (The University of Texas, Austin), James R. Walker, James B. Reeves, N. H. Nabbut, B. R. Byers, and R. J. Jones. Inoculum-dependent division lag of Bacillus cultures and its relation to an endogenous factor(s) ("schizokinen"). J. Bacteriol. 91:1070-1079. 1966.-When cells of Bacillus megaterium, grown on Brain Heart Infusion Agar, were inoculated into a chemically defined medium, they exhibited a division lag which was an inverse function of inoculum size. The addition of filtrates of cultures from the same medium eliminated the inoculum-dependent component of lag, but not an inoculum-independent residual lag of constant duration. Culture filtrate of B. subtilis var. niger not only eliminated its inoculum-dependent lag but also was required to sustain exponential division. Dose-response and "growth time" bioassays, developed to measure lag-reducing activity of filtrates, demonstrated accumulation of active filtrate factor to a "critical" concentration prior to division initiation. Addition of this concentration to cultures eliminated the inoculum-dependent lag. Accumulation of the factor ceased temporarily at onset of division, but excretion was resumed later during exponential growth. Accumulation of a lag-reducing, cell-associated factor followed a similar course. Chromatographic and bioautographic analyses of culture filtrates of B. megaterium indicated that a single substance was primarily responsible for their activity. Results of dose-response tests for reciprocal activities of filtrates of different Bacillus species and strains suggested production of different factors by some, and of different quantities of similar factors by others. It is proposed that such endogenous factors which are synthesized and accumulate to a population-dependent concentration as a requisite to initiation and maintenance of division be designated as "schizokinens."

Bacillus cereus↗
PubMedDate not supplied

Alcohol, drugs, and urban violence in a small city trauma center.

Substance abuse and urban trauma go hand in hand. But research focuses on large cities served by major academic medical centers. Do small cities face the same problems? Two hundred thirty-three urban trauma inpatients from a metro area of 250,000 were studied using patient interviews and medical records. As in large cities, one half used alcohol or drugs when attacked. Seventy percent were likely to be young, male, poor African-Americans. Only 3% were gang members, but demographic characteristics failed to explain substance abuse as they have for larger cities. A culture of violence pervades the small city, as it does in large urban ghettos. Two fifths were repeat urban trauma victims. Two fifths witnessed assaults in the past year. One third carried a knife or gun. Fifteen percent used a weapon on another person in the last year. Contextual variables, like being hurt in a bar, were related to drinking and drugs. The best predictor of present substance abuse and urban trauma was medical history of substance abuse. The need for (a) toxicology screens for all trauma victims, (b) referrals to substance abuse programs, (c) targeting at-risk populations for prevention, and (d) eliminating environments fostering violence and substance abuse is supported.

Adult↗
PubMedDate not supplied

Serum beta 2-microglobulin and interferon in homosexual males: relationship to clinical findings and serologic status to the human T lymphotropic virus (HTLV-III).

The identification of the human T cell lymphotropic virus (HTLV-III) as the presumed etiologic agent for AIDS has stimulated a re-examination and allowed better understanding of many of the immunologic abnormalities described in high risk individuals with and without clinical disease. Currently needed are useful predictors of clinical progression which will allow better counselling, earlier diagnosis and effective treatment of high risk individuals. We have examined the principles of test selection including sensitivity, specificity, predictive value and overall test efficiency for serum beta 2 microglobulin (beta 2M), serum interferon (IFN) and antibody to HTLV-III (HTLV-III Ab) in a group of 113 homosexual men and 62 controls. The presence of HTLV-III Ab and elevated serum beta 2M appear to be the most sensitive markers of immune dysregulation in the study group but also proved to be the least specific. Rising levels of serum beta 2M correlated with clinical severity where HTLV-III Ab positivity did not. The detection of elevated levels of acid labile serum IFN alpha was most specific for full-blown AIDS and was overall the most efficient test when compared with HTLV-III Ab, serum beta 2M and lymphocyte subpopulations. We believe that further examinations of the principles of test selection for immunologic abnormalities in AIDS may lead to potential applications for these tests in patient management.

Acquired Immunodeficiency Syndrome↗