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Biomedical subjects

D Perlman

Publications and source records attributed to D Perlman.

At least 73 records · Page 4Linked to original sources
PubMed1975

Transition of R factor NR1 in Proteus mirabilis: molecular structure and replication of NR1 deoxyribonucleic acid.

The structure of R factor NR1 DNA in Proteus mirabilis has been studied by using the techniques of CsCl density gradient centrifugation, sedimentation in neutral and alkaline sucrose gradients, and electron microscopy. It has been shown that the nontransitioned form of NR1 DNA isolated from P. mirabilis cultured in drug-free medium is a37-mum circular deoxyribonucleic acid (DNA) with a density of 1.712 g/ml in a neutral CsCl gradient. This circular molecule is a composite structure consisting of a 29-mum resistance transfer factor containing the tetracycline-resistance genes (RTF-TC) and an 8-mum r-determinants component conferring resistance to chloramphenicol (CM), streptomycin/spectinomycin, and the sulfonamides. There are one to two copies of NR1 per chromosome equivalent of DNA in exponential-phase cells cultured in Penassay broth. After growth of PM15/NR1 in medium containing 100 mug of CM per ml, the density of the NR1 DNA increased from 1.712 g/ml to approximately 1.718 g/ml and the proportion of NR1 DNA relative to the chromosome is amplified about 10-fold. The changes in R factor DNA structure which accompany this phenomenon (termed the transition) have been studied. DNA density profiles of the transitioned NR1 DNA consist of a 1.718 g/ml band which is skewed toward the less dense side. The transitioned NR1 DNA consists of molecules containing the RTF-TC element attached to multiple copies of r-determinants DNA (poly-r-determinant R factors) and multimeric and monomeric autonomous r-determinants structures. Poly-r-determinant R factors have a density intermediate between the basic composite structure (1.712 g/ml) and r-determinants DNA (1.718 g/ml). These species presumably account for the skewing of the 1.718-g/ml DNA band toward the less dense side. When transitioned cells are subsequently cultured in drug-free medium, poly-r-determinant R factors and autonomous poly-r-determinants undergo dissociation to form smaller structures containing fewer copies of r-determinants. This process continues until, after prolonged growth in drug-free medium the NR1 DNA returns to the nontransitioned state which consists of an RTF-TC and a single copy of r-determinants.

Chloramphenicol↗
PubMed1975

Denaturation mapping of R factor deoxyribonucleic acid.

The R factor NR1 consists of two components: a resistance transfer factor which harbors the tetracycline resistance genes (RTF-TC) and the r-determinants component which harbors the other drug resistance genes. Using partial denaturation mapping it is possible to distinguish the RTF-TC region from the r-determinants region of the composite R factor NR1 DNA which has a contour length of 37 mum and a density of 1.712 g/ml. The r-determinants region was a relatively undenatured 8.5-mum segment of the molecule when the deoxyribonucleic acid was partially denatured at pH 10.7. An RTF-TC genetic segregant of NR1 which had lost the r-determinants component had a contour length of 28.7 mum and a density of 1.710 g/ml. Characterization of an RTF-TC using partial denaturation mapping at pH 10.7 confirmed that the relatively undenatured 8.5-mum r-determinants segment of the composite R factor had been deleted. Circular, transitioned NR1 DNA molecules (1.716 to 1.718 g/ml), whose contour lengths were consistent with an RTF-TC plus an integral number of tandem copies of r-determinants, were also characterized by denaturation mapping. The relatively undenatured region in these molecules had a length equal to an integral number of copies of r-determinants and was located at the same site in the partially denatured RTF-TC as the single copy of r-determinants in the 37-mum composite NR1. This indicates that there is a unique integration site for r-determinants in the RTF-TC component. The R factor UCR122, a TC deletion mutant of NR1, was also characterized by denaturation mapping. The translocation of the TC resistance gene(s) on the denaturation map permitted the alignment of the denaturation map with the heteroduplex map of Sharp et al. (u073). Linear and circular monomeric and presumed multimeric r-determinants DNA molecules (p = 1.718 g/ml) were partially denatured at a higher pH (11.10). The r-determinants multimers showed a repeating 8.3-mum (monomeric) partial denaturation pattern indicating a head-to-tail arrangement of monomers in these poly-r-determinant molecules.

DNA, Bacterial↗
PubMed1975

Microbial degradation of erythromycins A and B.

Growing cultures, as well as broken and lyophilized cells of pseudomonas 56 were found to degrade erythromycin A, and lyophilized cells inactivated erythromycins A and B. The enzyme system involved in this degradation was constitutive and the enzyme level in the cells could be increased about 8-fold when oleandomycin or erythromycin B was added to the growth medium. The ability of whole or broken cells to inactivate erythromycin A was completely lost when these preparations were boiled, and the erythromycin A-inactivating activity was localized in the cell membrane fraction. The lyophilized cells did not degrade oleandomycin, methymycin, tylosin, a mixture of leucomycins, josamycin, or maridomycin III.

Anti-Bacterial Agents↗
PubMed1975

Characteristics of two broad spectrum antibiotics produced by Mycoplasma sp. RP III.

Two extracellular antibiotics produced by Mycoplasma sp. RP III growing in serum-containing media have been purified by solvent extraction and ion-exchange chromatography. Factor I inhibits Gram-positive and Gram-negative bacteria in vitro and a crude preparation protected mice from Pseudomonas and Straphylococcus infections; it is of low cytotoxicity. Factor II, a lipid, inhibits Gram-positive and Gram-negative bacteria, Candida species, and is as cytotoxic as the actinomycins.

Animals↗