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Biomedical subjects

D Perlman

Publications and source records attributed to D Perlman.

At least 55 records · Page 3Linked to original sources
PubMed1977

Selective amplification of genes on the R plasmid, NR1, in Proteus mirabilis: an example of the induction of selective gene amplification.

The drug-resistance plasmid, NR1, is a 37-micron circular DNA molecule that contains two components: the resistance transfer factor (29 micron) carrying the transfer genes and the genes for tetracycline resistance, and the r-determinant (8 micron) carrying the genes for resistance to several other antibiotics including chloramphenicol (Cm). In Proteus mirabilis, these two components are capable of independent replication, or they may replicate as a composite molecule. When cells of P. mirabilis containing NR1 are cultured in medium containing Cm at 250 microgram/ml a growth lag of 20-35 hr ensues. During this lag, Cm induces the selective amplification of the r-determinant, including the gene for resistance to Cm. The amplification results from the excision of the r-determinant from the R plasmid, the independent replication of the r-determinant to give polymeric as well as monomeric r-determinants, and the eventual reintegration of multiple tandem copies of the r-determinant with the resistance transfer factor to form a new R plasmid with multiple copies of the r-determinant. This mechanism represents a new level of control of gene expression in bacterial systems--namely, the induction of selective gene amplification.

Cell Division↗
PubMed1977

Microbial production of vitamin B12 antimetabolites. III Compound 102804 from Bacillus cereus.

A basic compound with empirical formula C12H16N2O5 was isolated from Bacillus cereus 102804 fermentations of a soybean meal-glucose medium. The inhibitory activity of compound 102804 on growth of Gram-positive and Gram-negative bacteria growing in a chemically defined medium was reversed by vitamin B12, by L-methionine, and by D-methionine. It has no inhibitory activity for Escherichia coli (Davis 113-3) when grown in media containing L-methionine. The biosynthesis of 102804 coincides with the sporulation of the B. cereus, and the compound is not produced in the absence of sporulation.

Antimetabolites↗
PubMed1976

Conversion of L-sorbose to L-sorbosone by immobilized cells of Gluconobacter melanogenus IFO 3293.

Gluconobacter melanogenus IFO 3293 cells capable of converting L-sorbose to L-sorbosone were immobilized in polyacrylamide gel. The preferred polymer composition for high activity and stability was determined to contain a total monomer concentration of 7.2% and 16.6% crosslinking agent. No significant differences in optimal conditions for conversion, e.g., pH and temperature, were found in comparison with free cell suspensions. However, in the absence of L-sorbose, the thermal stability of immobilized cells was lower. After the initial loss, the conversion activity of immobilized cells increased, possibly due to lysis, and this increase was related to the polymerization conditions and the incubation temperature for the L-sorbose conversion. The enzymatic activity and stability of the immobilized cells also depended on the physical form of the gel and the aeration levels. Addition of electron acceptors or addition of L-sorbosone to the medium reduced, while addition of neomycin, ampicillin, chloramphenicol, and tetracycline increased the stability of the enzymatic activity.

Electron Transport↗
PubMed1975

Accumulation of replicating bacterial plasmid DNA during thymine limitation or hydroxyurea treatment.

The rate of DNA chain elongation of a thymine auxotroph of Proteus mirabilis harboring an R factor was reduced by either thymine limitation or treatment with hydroxyurea. Using CsCl density gradient centrifugation, sedimentation in sucrose gradients, and electron microscopy, it has been shown that the fraction of total R factor DNA which is in the process of replication is greatly increased when the rate of DNA chain elongation is reduced while the initiation of plasmid replication continues at the normal rate. This makes possible the isolation and characterization of replicating plasmid DNA. Electron microscopy revealed that replicating R factor DNA consists of double-branched (theta type) circular molecules.

Centrifugation, Density Gradient↗
PubMed1975

Stimulation by organic solvents and detergents of conversion of L-sorbose to L-sorbosone by Gluconobacter melanogenus IFO 3293.

Treatment of Gluconobacter melanogenus IFO 3293 cells with benzene, carbon tetrachloride, cyclohexane, deoxycholate, toluene, or xylene stimulated their conversion of L-sorbose to L-sorbosone two- to threefold. The degree of stimulation depended upon the length of exposure time to the agent and the age of the G. melanogenus cells. A rapid decrease in viability of the cells and degradation of cell RNA was noted after treatment with the effective agents. The G. melanogenus cells were unable to absorb L-sorbose actively after toluene treatment.

Age Factors↗
PubMed1975

Volunteer bias and personality traits in sexual standards research.

The effects of personality traits and volunteer bias in sexual standards research were studied. Two hundred and fifty-four subjects completed Jackson's Personality Research Form (PRF) and were subsequently sent either a sex or a control questionnaire. Return rates for the two groups were comparable. Also, the analyses of the PRF scores failed to show sex volunteers as having unique personality characteristics. These results are interpreted as grounds for rejecting the widely held stereotype that volunteers for sexual standards surveys are inevitably an atypical, deviant group. The possible limiting effects of age and method of soliciting information are discussed.

Adult↗