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Biomedical subjects

A Rich

Publications and source records attributed to A Rich.

At least 289 records · Page 16Linked to original sources
PubMed1981

7-Methylguanine in poly(dG-dC).poly(dG-dC) facilitates z-DNA formation.

Poly(dG-dC).poly(dG-dC) was methylated at the N-7 position of guanine through the use of dimethyl sulfate. The conversion of poly(dG-dC).poly(dG-dC) from B-DNA to the Z-DNA form was followed by measuring both the circular dichroic spectra and changes in the absorbance ratio A295/A260. Increasing methylation steadily decreases the amount of NaCl or MgCl2 that is required to convert the polymer from B-DNA to Z-DNA. At 100% methylation of the guanine residues, the modified polymer is fully converted to Z-DNA in a physiological salt solution. Kinetic experiments show that methylation markedly accelerates the speed of the conversion from B-DNA to Z-DNA in the presence of added salt. These effects may be partly due to the positive charge on guanine that accompanies N-7 methylation.

Base Sequence↗
PubMed1981

Anomalous preferences of cultured macrophages for hydrophobic and roughened substrata.

Peritoneal macrophages were plated out on a series of artificial haptotactic substrata consisting of grid patterns of vacuum-evaporated palladium metal alternating with hydrophobic untreated polystyrene and with hydrophilic sulphonated polystyrene. By their active locomotion the macrophages accumulated preferentially onto the less hydrophilic of either pair of these alternative substrata. This order of substratum preference is precisely the opposite to that shown by fibroblastic cells. Macrophages were also found to accumulate preferentially onto roughened culture surfaces as opposed to smooth ones, which is again opposite to the behaviour of fibroblasts. These opposite substratum preferences shown by macrophages may reflect physical as well as functional differences in their surfaces, and could serve as assay criteria for macrophages and cell types putatively equivalent to macrophages.

Animals↗
PubMed1980

Biochemical and structural studies of the tetragonal crystalline modification of the Escherichia coli elongation factor Tu.

The tetragonal crystalline form of the trypsin-treated Escherichia coli protein elongation factor Tu has been analyzed by biochemical and x-ray crystallographic techniques. The crystals contain two tightly associated polypeptide fragments of molecular weight 36,000 and 6,500 which represent 97% of the native enzyme. The crystals do not contain a short internal polypeptide fragment of 14 amino acids which dissociates from the native enzyme following mild trypsin digestion. The short fragment has been implicated in the aminoacyl-tRNA binding function and its location has been determined. The structure of the modified enzyme in the P4(3)2(1)2 crystal form has been determined to 5 A resolution by x-ray diffraction methods. The protein consists of two domains: the larger domain exhibits considerable alpha helical characteristics and the smaller domain has no identifiable secondary structural features. The relationship between the double domain structure of the enzyme and its biochemical properties is discussed.

Bacterial Proteins↗
PubMed1980

Three-dimensional structure of Escherichia coli initiator tRNAfMet.

The crystal structure of Escherichia coli tRNAfMet an initiator transfer RNA, has been determined. While grossly similar to that of the chain-elongating yeast tRNAPhe, there are three major differences. One involves the folding of the anticodon loop; in particular, the position of the constant uridine, U33. This difference was unexpected and may be of functional significance.

Anticodon↗
PubMed1980

Peptide inhibitors of sickle hemoglobin aggregation: effect of hydrophobicity.

Thirty-three peptides have been synthesized which have the ability to inhibit aggregation of sickle hemoglobin which occurs upon deoxygenation. Evidence is presented which indicates that the hydrophobicity of the side chains is the predominant factor. A linear correlation exists between the capacity of peptides to inhibit gelation and the additivity of the side-chain hydrophobic contributions. Small di- and tri-peptides are more responsive to changes in their nonpolar content than are larger oligopeptides whose antigelling activity is a slowly varying function of hydrophobicity. With few exceptions, charged substituent groups on the side chain do not appear to contribute to the inhibitory process. Thus, if hydrogen bonding or ionic interactions are involved with these residues, they appear to play only a secondary role in the molecular interactions responsible for inhibiting or delaying the deoxy-HbS gelation.

Calorimetry↗
PubMed1980

X-ray diffraction studies on crystalline complexes of the gene 5 DNA-unwinding protein with deoxyoligonucleotides.

Complexes of the gene 5 protein with a variety of oligodeoxynucleotides, ranging in length from two to eight and having several different sequences, have been formed and crystallized for x-ray diffraction analysis. The crystallographic parameters of four different unit cells, all of which are based on hexagonal packing arrangements, indicate that the fundamental unit of the complex is composed of 12 gene 5 monomers.

Crystallization↗
PubMed1980

A UGA termination suppression tRNATrp active in rabbit reticulocytes.

A tRNATrp was purified from rabbit reticulocytes which suppresses the UGA termination codon of beta-haemoglobin mRNA. Evidence is presented that the beta-haemoglobin readthrough protein is found in reticulocyte translations and intact cells. Some natural readthrough proteins perform essential functions; they are synthesised through suppression of UGA or UAG but not UAA termination codons.

Animals↗
PubMed1980

Translational control of protein synthesis in response to heat shock in D. melanogaster cells.

In response to elevated temperature, Drosophila cells synthesize a small set of proteins known as the heat-shock proteins, while synthesis of most other proteins ceases. In vitro translation has been used to demonstrate that the messenger RNAs encoding the normal (25 degrees) spectrum of proteins are not broken down or irreversibly inactivated in response to the temperature change. During the heat shock only the heat-shock mRNAs plus a small number of preexisting mRNAs are translated, while most other messages are stored and can be reactivated upon return of the cells to their normal temperature. After recovery from heat shock, cells translate both the normal mRNA and the remaining heat-shock mRNA. The translational control operating in intact cells has been reproduced in cell-free translation systems directed by purified mRNA from normal and heat-shocked cells. Lysates prepared from heat-shocked Drosophila cells preferentially translated the heat-shock messages, while the lysate made from normally growing Drosophila cells indiscriminately translated both normal and heat-shock messages. Therefore there must be stable alterations in the translational components of heat-shocked cells which are capable of causing selective translation of the heat-shock messages. In addition there must be information encoded in the heat-shock messages that allows their selection.

Animals↗
PubMed1980

The structure of a DNA unwinding protein and its complexes with oligodeoxynucleotides by x-ray diffraction.

The structure of the gene 5 DNA unwinding protein from bacteriophage fd has been solved to 2.3 A resolution by x-ray diffraction techniques. The molecule contains an extensive cleft region that we have identified as the DNA binding site on the basis of the residues that comprise its surface. The interior of the groove has a rather large number of basic amino acid residues that serve to draw the polynucleotide backbone into the cleft. Arrayed along the external edges of the groove are a number of aromatic amino acid side groups that are in position to stack upon the bases of the DNA and fix it in place. The cleft then acts as an elongated pair of jaws that draws the DNA between them by charge interactions involving the phosphates with the interior lysines and arginines. The jaws then close on the DNA strand through small conformation changes and the rotation of aromatic side-chains into position to stack upon the purines and pyrimidines. Complexes of the gene 5 protein with a variety of oligodeoxynucleotides have been formed and crystallized for x-ray diffraction analysis. The crystallographic parameters of four different unit cells indicate that the fundamental unit of the complex is composed of six gene 5 protein dimers. We believe this aggregate has 622 point group symmetry and is a ring formed by end to end closure of a linear array of six dimers. From our results we have proposed a double helical model for the gene 5 protein-DNA complex in which the protein forms a spindle or core around which the DNA is spooled. 5.0-A x-ray diffraction data from one of the crystalline complexes is currently being analyzed by molecular replacement techniques to obtain what we believe will be the first direct visualization of a protein-deoxyribonucleic acid complex approaching atomic resolution.

Coliphages↗
PubMed1980

Antisickling activity of amino acid benzyl esters.

The sickling of homozygous sickel cells upon deoxygenation is inhibited in the presence of 3 mM L-phenylalanine benzyl ester (Phe-OBzl) or benzyl esters of other aromatic or hydrophobic amino acids. Phe-OBzl was found to permeate into erythrocytes rapidly, and the deoxygenated cells maintained considerable flexibility as measured by their ability to pass through 3-micron pores. The osmotic fragility of the cells was unchanged and the oxygen dissociation curve was shifted slightly from a 50% saturation values of 28.5 mm Hg to 31.0 mm Hg. At lower concentrations of Phe-OBzl some antisickling activity was seen. The Phe-OBzl antisickling activity may involve both binding to deoxyhemoglobin S and modification of the erythrocyte membrane. This class of compounds has considerable potential as therapeutic agents for the treatment of sickle cell disease.

Amino Acids↗
PubMed1980

Molecular structure of an anticancer drug-DNA complex: daunomycin plus d(CpGpTpApCpG).

The structure of the crystalline daunomycin-d(CpGpTpApCpG) complex has been solved by x-ray diffraction analysis. The DNA forms a six-base-pair right-handed double helix with two daunomycin molecules intercalated in the d(CpG) sequences. The daunomycin aglycone chromophore is oriented at right angles to the long dimension of the DNA base pairs and the cyclohexene ring rests in the minor groove. Substituents on this ring have hydrogen bonding interactions to the base pairs above and below the intercalation site. These appear to be specific for anthracycline antibiotics. The amino sugar lies in the minor groove of the double helix without bonding to the DNA. The DNA double helix is distorted in a novel manner in accommodating the drug.

Daunorubicin↗
PubMed1980

The tetramer d(CpGpCpG) crystallizes as a left-handed double helix.

The structure of the tetramer d(CpGpCpG) has been solved by x-ray analysis in two different crystal forms with and without spermine cations. The molecules crystallize in hexagonal unit cells and they form a left-handed double helix of Z-DNA similar to that previously reported for the hexamer d(CpGpCpGpCpG). In the crystal lattice the molecules stack together to form a virtually continuous left-handed double helix in which every fourth phosphate group is missing. The stacking of bases upon each other is similar to that seen in the hexamer. However, the base pairs have a slightly different orientation in that the cytosine residues are slightly removed from the axis of the molecule compared to the position they occupy in the hexamer. The structures are similar in two crystal forms with and without spermine cations.

Base Sequence↗
PubMed1980

Biosynthesis of parathyroid hormone.

Figure 11 summarizes our present concepts of the biosynthetic sequence for parathyroid hormone, deduced largely from observations in vitro. Many aspects of the presumed process whereby preproparathyroid hormone is converted via proparathyroid hormone to the hormone remain unclarified and require much further study, as is true for many other prehormones. These studies, however, coupled with (1) further investigations of intracellular degradation of parathyroid hormone, if this indeed operates in vivo; (2) the proteolytic conversion of secreted hormone in peripheral tissues; and (3) analysis of transcriptional control of biosynthesis of parathyroid hormone, using radioactive cDNA for hybridization studies of mRNA production and turnover, hold great promise for further understanding of critical regulatory factors central to expression of the actions of parathyroid hormone.

Adenylyl Cyclases↗
PubMed1979

Stability of the unique anticodon loop conformation of E.coli tRNAfMet.

Initiator tRNAs have an anticodon loop conformation distinct from that of elongation tRNAs as detected by susceptibility to S1 nuclease. We now find the anticodon loop conformation of E. coli tRNAfMet to be stable under different salt conditions as detected by using S1 nuclease as a structural probe. In contrast, a conformational change is observed in the T- and D- loop of this tRNA in the absence of added Mg2+. This change can be suppressed by spermine. Even under those conditions effecting a change in T- and D- loop conformation, the anticodon loop does not change. This suggests that the conformational shift is controlled by Mg2+ and restricted to the D- and T- loop region only without affecting the anticodon domain. The use of S1 nuclease as a conformational probe requires the use of kinetic studies to determine the initial cleavage sites. Thus, the use of a strong inhibitor which immediately stops the action of this nuclease is necessary. ATP is shown to be such an inhibitor.

Anticodon↗
PubMed1979

Conformational changes of yeast tRNAPhe and E. coli tRNA2Glu as indicated by different nuclease digestion patterns.

The susceptibility of yeast tRNAPhe and Escherichia coli tRNA2Glu to digestion by nucleases Tl and Sl are examined in a variety of environments, and the results are interpreted in view of the available three-dimensional structural information. Significant differences are found in the digestion pattern of the two tRNAs using the guanosine-specific Tl nuclease. In particular, differences are seen due to varying the type of salts in the environment. However, the Sl nuclease results on the two tRNAs do not differ greatly. E. coli tRNA2Glu is known to exist in two different conformations. Nuclease digestion results are presented revealing differences which make it possible to draw some inferences about the structural differences in these two conformations. In carrying out these analyses, the tRNA molecules are labeled either by putting 32P at the 5'-end of the molecular or by adding 32P-labeled pCp at the 3'-end. It is found that both yeast tRNAPhe and E. coli tRNA2Glu have modified Tl nuclease digestion patterns when pCp is added at the 3'-end of the molecule.

Alkaline Phosphatase↗