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Biomedical subjects

M J Solomon

Publications and source records attributed to M J Solomon.

104 records · Page 6Linked to original sources
PubMed1987

The yeast ubiquitin genes: a family of natural gene fusions.

Ubiquitin is a 76-residue protein highly conserved among eukaryotes. Conjugation of ubiquitin to intracellular proteins mediates their selective degradation in vivo. We describe a family of four ubiquitin-coding loci in the yeast Saccharomyces cerevisiae. UB11, UB12 and UB13 encode hybrid proteins in which ubiquitin is fused to unrelated ('tail') amino acid sequences. The ubiquitin coding elements of UB11 and UB12 are interrupted at identical positions by non-homologous introns. UB11 and UB12 encode identical 52-residue tails, whereas UB13 encodes a different 76-residue tail. The tail amino acid sequences are highly conserved between yeast and mammals. Each tail contains a putative metal-binding, nucleic acid-binding domain of the form Cys-X2-4-Cys-X2-15-Cys-X2-4-Cys, suggesting that these proteins may function by binding to DNA. The fourth gene, UB14, encodes a polyubiquitin precursor protein containing five ubiquitin repeats in a head-to-tail, spacerless arrangement. All four ubiquitin genes are expressed in exponentially growing cells, while in stationary-phase cells the expression of UB11 and UB12 is repressed. The UB14 gene, which is strongly inducible by starvation, high temperatures and other stresses, contains in its upstream region strong homologies to the consensus 'heat shock box' nucleotide sequence. Elsewhere we show that the essential function of the UB14 gene is to provide ubiquitin to cells under stress.

Amino Acid Sequence↗
PubMed1987

A nuclease-hypersensitive region forms de novo after chromosome replication.

Regular nucleosome arrays in eucaryotic chromosomes are punctuated at specific locations, such as active promoters and replication origins, by apparently nucleosome-free sites, also called nuclease-hypersensitive, or exposed, regions. The -400-base pair-exposed region within simian virus 40 (SV40) chromosomes is present in approximately 20% of the chromosomes in lytically infected cells and encompasses the replication origin, transcriptional enhancer, and both late and early SV40 promoters. We report that nearly all SV40 chromosomes lacked the exposed region during replication and that newly formed chromosomes acquired the exposed region of the same degree as did bulk SV40 chromosomes within 1 h after replication. Furthermore, a much lower but significant level of exposure was detectable in late SV40 replication intermediates, indicating that formation of the exposed region could start within minutes after passage of the replication fork.

Chromatin↗
PubMed1986

A mammalian high mobility group protein recognizes any stretch of six A.T base pairs in duplex DNA.

alpha-Protein is a high mobility group protein originally purified from African green monkey cells based on its affinity for the 172-base-pair repeat of monkey alpha-satellite DNA. We have used DNase I footprinting to identify 50 alpha-protein binding sites on simian virus 40 DNA and thereby to determine the DNA binding specificity of this mammalian nuclear protein. alpha-Protein binds with approximately equal affinity to any run of six or more A X T base pairs in duplex DNA, to many, if not all, runs of five A X T base pairs, and to a small number of other sequences within otherwise (A + T)-rich regions. Unlike well characterized sequence-specific DNA binding proteins such as bacterial repressors, alpha-protein makes extensive contacts within the minor groove of B-DNA. These and related findings indicate that, rather than binding to a few specific DNA sequences, alpha-protein recognizes a configuration of the minor groove characteristic of short runs of A X T base pairs. We discuss possible functions of alpha-protein and the similarities in DNA recognition by alpha-protein and the antibiotic netropsin.

Animals↗
PubMed1985

In vivo effects of cis- and trans-diamminedichloroplatinum(II) on SV40 chromosomes: differential repair, DNA-protein cross-linking, and inhibition of replication.

The mechanism of action of the antitumor drug cis-diamminedichloroplatinum(II), cis-DDP, was investigated by using the approximately 5200 base pair (bp) chromosome of simian virus 40 (SV40) as an in vivo chromatin model. Comparative studies were also carried out with the clinically ineffective isomer trans-DDP. Although 14 times more trans- than cis-DDP in the culture medium is required to inhibit SV40 DNA replication in SV40-infected green monkey CV-1 cells, the two isomers are equally effective at inhibiting replication when equimolar amounts are bound to SV40 DNA in vivo. Since both isomers are transported into CV-1 cells at similar rates, differential uptake cannot account for the greater ability of cis-DDP to inhibit SV40 DNA replication. Rather, this result is explained by the finding that cis-DDP-DNA adducts accumulate continuously over the incubation period, whereas trans-DDP binding to DNA reaches a maximum at 6 h and thereafter decreases dramatically. We suggest that the different accumulation behavior of cis-DDP and trans-DDP on DNA is due to their differential repair in CV-1 cells. A variety of non-histone proteins, including SV40 capsid proteins but virtually no histones, are cross-linked to SV40 DNA in vivo by either cis- or trans-DDP. More DNA-protein cross-links are formed by trans-DDP than by cis-DDP at equivalent amounts of DNA-bound platinum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Formaldehyde-mediated DNA-protein crosslinking: a probe for in vivo chromatin structures.

Formaldehyde (HCHO) produces DNA-protein crosslinks both in vitro and in vivo. Simian virus 40 (SV40) chromosomes that have been fixed by prolonged incubation with HCHO either in vitro or in vivo (within SV40-infected cells) can be converted to nearly protein-free DNA by limit-digestion with Pronase in the presence of NaDodSO4. The remaining Pronase-resistant DNA-peptide adducts retard the DNA upon gel electrophoresis, allowing resolution of free and crosslink-containing DNA. Though efficiently crosslinking histones to DNA within nucleosomes both in vitro and in vivo, HCHO does not crosslink either purified lac repressor to lac operator-containing DNA or an (A + T)-DNA-binding protein (alpha-protein) to its cognate DNA in vitro. Furthermore, a protein that does not bind to DNA, such as serum albumin, is not crosslinked to DNA by HCHO even at extremely high protein concentrations. These properties of HCHO as a DNA-protein crosslinker are used to probe the distribution of nucleosomes in vivo. We show that there are no HCHO-crosslinkable DNA-protein contacts in a subset of SV40 chromosomes in vivo within a 325-base-pair stretch that spans the "exposed" (nuclease-hypersensitive) region of the SV40 chromosome. This replication origin-proximal region has been found previously to lack nucleosomes in a subset of isolated SV40 chromosomes. We discuss other applications of the HCHO technique, including the possibility of obtaining base-resolution in vivo nucleosome "footprints."

Animals↗
PubMed1978

Optimal nutritional support in surgery for bladder cancer: preservation of visceral protein by amino acid infusions.

Seventeen patients undergoing 19 major urological operations for bladder cancer or rectal leiomyosarcoma (1 case) were studied after randomization for 3 hypocaloric dietary regimens, preoperative keto-adaptation by a carbohydrate-free, oral protein diet continued in the postoperative period by isotonic amino acid infusions, postoperative amino acid infusions only and 5 per cent dextrose infusions. In these normally nourished patients serum transferrin (plus 13 mg./dl. minus 30 mg./dl., minus 69 mg./dl., p less than 0.05 for the first and combined amino acid groups against the third group) and 2 other short half-life hepatic secretory proteins, prealbumin and retinol-binding protein, represented sensitive indexes of visceral protein and nutritional support, superior to nitrogen balance, anthropometric assays, delayed hypersensitivity skin test reactivity and serum albumin. Near isotonic amino acid infusions were more effective in preserving visceral protein status than 5 per cent dextrose but preoperative keto-adaptation was not shown to have any increased benefit over protein-sparing therapy given only after an operation.

Aged↗
PubMedDate not supplied

Difficult clinical decisions in gynecological oncology: identifying priorities for future clinical research.

This study investigates the acceptability and feasibility of conducting randomized controlled trials (RCTs) in gynecological oncology by ascertaining the views of the Australian Society of Gynaecologic Oncologists (ASGO) about important clinical questions in this field, current treatment preferences, and willingness to participate in trials to address these questions. Members of ASGO received a mailed survey. Thirty-one gyneoncologists participated in this study (79% response fraction). There was considerable support for an RCT (81%; 95% confidence interval [CI], 63-93%) to compare sentinel node biopsy with total groin dissection for women with vulval cancer. This clinical question was also rated as "extremely" or "very" important by 91% (95% CI, 74-98%) of respondents, who also indicated high levels of individual equipoise. Another priority for research involved the use of second-line chemotherapy for women who have rising CA125 titers. This clinical question was rated as extremely or very important by 71% (95% CI, 52-86%), exhibited high levels of individual equipoise, with 74% (95% CI, 55-88%) of respondents willing to participate in an RCT to address this issue. The conduct of surveys of representative groups of clinicians provides useful empirical data to focus clinical research efforts where they are most likely to be successful based on equipoise, feasibility, and clinical interest.

Adult↗