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M M Seidman

Publications and source records attributed to M M Seidman.

58 records · Page 4Linked to original sources
PubMed1977

Chromatin fractionation related to cell type and chromosome condensation but perhaps not to transcriptional activity.

A chromatin fractionation procedure has been developed that involves the shearing of swollen chromatin and the separation of chromatin fragments by sucrose gradient centrifugation. When chromatin from rapidly growing HeLa cells was fractionated, four partially resolved peaks were obtained. Partial characterization of the chromatin fractions indicated that each contained similar lengths of DNA formed in a complex with histones in nucleosomes. The most likely difference between the fractions is the degree of intra-or interstrand association of the fibers of nucleosomes. Chromatins from chicken erythrocytes and mitotic chromosomes were analyzed by the procedure. These chromatins yielded gradient profiles that were distinctly different from each other and from interphase chromatin. These results suggested that the fractionation procedure reflected at least some of the differences in the structure of chromatin known to exist in vivo. The association of pulse-labeled RNA with a particular chromatin fraction is frequently used to support claims of successful separation of transcriptionally active chromatin from inactive chromatin. Since our data show that the slowly sedimenting fractions preferentially bind RNA whose synthesis was clearly not in progress at the start of the fractionation, this criterion is suspect. The presence of equal amounts of satellite DNA in all fractions of mouse L-cell chromatin indicated that the method did not fractionate on the basis of the in vivo transcriptional activity.

Animals↗
PubMed1969

Influence of side-chain substituents on the position of cleavage of the benzene ring by Pseudomonas fluorescens.

Pseudomonas fluorescens was grown on mineral salts media with phenol, p-hydroxybenzoic acid, p-hydroxy-phenylacetic acid, or p-hydroxy-trans-cinnamic acid as sole carbon and energy source. Each compound was first hydroxylated, ortho to the hydroxyl group on the benzene ring, to give catechol, protocatechuic acid (3,4-dihydroxy-benzoic acid), homoprotocatechuic acid (3,4-dihydroxy-phenylacetic acid), and caffeic acid (3,4-dihydroxy-trans-cinnamic acid), respectively, as the ultimate aromatic products before cleavage of the benzene nucleus. Protocatechuic acid and caffeic acid were shown to be cleaved by ortho fission, via a 3,4-oxygenase mechanism, to give beta-substituted cis, cis-muconic acids as the initial aliphatic products. However, catechol and homoprotocatechuic acid were cleaved by meta fission, by 2,3-and 4,5-oxygenases, respectively, to give alpha-hydroxy-muconic semialdehyde and alpha-hydroxy-gamma-carboxymethyl muconic semialdehyde as initial aliphatic intermediates. Caffeic acid: 3,4-oxygenase, a new oxygenase, consumes 1 mole of O(2) per mole of substrate and has an optimal pH of 7.0. The mechanism of cleavage of enzymes derepressed for substituted catechols by P. fluorescens apparently changes from ortho to meta with the increasing nephelauxetic (electron donor) effect of the side-chain substituent.

Benzene Derivatives↗
PubMedDate not supplied

Use of supF, an Escherichia coli tyrosine suppressor tRNA gene, as a mutagenic target in shuttle-vector plasmids.

The Escherichia coli tyrosine amber suppressor tRNA gene, supF, has been utilized as a mutagenic target in several shuttle-vector plasmids. Data on mutagenic inactivation of suppressor activity was obtained from induced mutagenesis experiments with plasmids pZ189 and p3AC, and from studies on alterations of the supF gene transduced into E. coli. 162 single or tandem base-substitution mutations that reduce or eliminate suppressor activity were identified at 86 sites within 158 base pairs. The 2 transition and 4 transversion mutations possible in double-stranded DNA were all detectable. At 56 sites two different inactivating mutations were found; and at 20 sites all 3 possible base substitution mutations inactivated suppressor function. Most of the mutations were clustered within the mature tRNA region: 144 of the base-substitution mutations were found at 74 sites within the 85-bp mature tRNA region. Insertions of 1 or 2 bases at 4 sites and deletions of 1 to 3 bases at 15 sites were found to inactivate supF function. A few silent mutations which do not inactivate suppressor function were found: single base-substitutions at 4 sites, 14 pairs of silent double mutations, and a large deletion including the promoter region. The supF gene is thus an extremely sensitive target for mutagenic inactivation in shuttle-vector plasmids.

Base Sequence↗