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At least 19 recordsLinked to original sources
PubMed1977

A comparison of small circular DNA molecules in psi+ and psi- strains of Saccharomyces cerevisiae.

The psi+ and psi- phenotypes, which affect the efficiency of ochre suppression in yeast, are inherited in a non-Mendelian fashion. There is no apparent difference in length or in length distribution of 2 micronm circular DNA molecules between psi+ and psi- strains. It seems that the psi genetic determinant is probably not connected with the presence or absence of these small circular DNA molecules.

DNA, Circular↗
PubMed1977

Rabbit liver tRNA1Val:II. unusual secondary structure of T psi C stem and loop due to a U54:A60 base pair.

In contrast to all other known tRNAs, mammalian tRNA1Val contains two adenosines A59 and A60, opposite to U54 and psi 55 in the U psi CG sequence of the T psi C loop, which could form unusual A:U (or A: psi pairs in addition to the five "normal" G:C pairs. In order to measure the number of G:C and A:U (A: psi) pairs in the T psi C stem, we prepared the 30 nucleotide long 3'-terminal fragment of this tRNA by "m7G-cleavage". From differentiated melting curves and temperature jump experiments it was concluded that the T psi C stem in this fragment is in fact extended by an additional A60:U54 pair. A dimer of this fragment with 14 base pairs was characterized by gel electrophoresis and by the same physical methods. An additional A:U pair in the tRNA1Val fragment does not necessarily mean that this is also true for intact tRNA. However, we showed that U54 is far less available for enzymatic methylation in mammalian tRNA1Val compared to tRNA from T-E. coli. This clear difference in U54 reactivity, together with the identification of an extra A60:U54 pair in the U psi CG containing fragment suggests the presence of a 6 base pair T psi C stem and a 5 nucleotide T psi C loop in this tRNA.

Adenine Nucleotides↗
PubMed1979

Empirical torsional potential functions from protein structure data. Phi- and psi-potentials for non-glycyl amino acid residues.

The torsional potential functions Vt(phi) and Vt(psi) around single bonds N--C alpha and C alpha--C, which can be used in conformational studies of oligopeptides, polypeptides and proteins, have been derived, using crystal structure data of 22 globular proteins, fitting the observed distribution in the (phi, psi)-plane with the value of Vtot(phi, psi), using the Boltzmann distribution. The averaged torsional potential functions, obtained from various amino acid residues in L-configuration, are Vt(phi) = 1.0 cos (phi + 60 degrees); Vt(psi) = 0.5 cos (psi + 60 degrees) - 1.0 cos (2 psi + 30 degrees) - 0.5 cos (3 psi + 30 degrees). The dipeptide energy maps Vtot(phi, psi) obtained using these functions, instead of the normally accepted torsional functions, were found to explain various observations, such as the absence of the left-handed alpha helix and the C7 conformation, and the relatively high density of points near the line psi = 0 degrees. These functions derived from observational data on protein structures, will, it is hoped, explain various previously unexplained facts in polypeptide conformation.

Amino Acid Sequence↗
PubMed1977

The extrachromosomal control of nonsense suppression in yeast: an analysis of the elimination of [psi+] in the presence of a nuclear gene PNM.

When a [psi-] strain of yeast mutates to [psi+], the efficiency of suppression by certain ochre suppressors is increased. The [psi+] phenotype is inherited extrachromosomally. There is a nuclear gene, PNM, which, when mutant, causes loss of the [psi+] phenotype. PNM- is dominant to PNM+ and a heterozygous diploid gradually loses the ability over successive generations, to produce PNM+ [psi+] spores. This paper describes the kinetics of this elimination and the data obtained are discussed in relation to two models of the molecular nature of the [psi] genetic determinant--one considering the [psi] determinant as an autonomous nucleic acid, the other treating the possibility that the [psi] nucleic acid is that which codes for rRNA in the nuclear genome.

Cell Division↗
PubMed2026

Research progress on the regulatory mechanisms of the PSY promoter.

Carotenoids are essential pigments in the plant photosynthetic apparatus, functioning in light harvesting, photoprotection, and signal transduction, and serving as precursors of vital nutrients such as vitamin A. Phytoene synthase (PSY) is the first rate-limiting enzyme in the plant carotenoid biosynthetic pathway, and its transcriptional regulation primarily depends on cis-acting promoter elements, associated transcription factors, and epigenetic status. The PSY promoter region contains core cis-elements as well as multiple light-, hormone-, and stress-responsive elements, which collectively function as key regulatory sites governing spatiotemporal expression. This review systematically summarizes recent advances in PSY promoter regulation by plant hormones (e.g., abscisic acid, ethylene, jasmonic acid), environmental factors (light signaling, temperature, salinity, and drought), and epigenetic mechanisms (DNA methylation, histone modifications, and chromatin remodeling). In addition, the application of transgenic and biotechnological approaches to PSY promoter regulation is further summarized. Including promoter sequence engineering with precise editing of cis-elements and promoter-targeted CRISPR activation/interference (CRISPRa/i) for tunable transcriptional control. Emphasis is placed on how these signals are integrated at the promoter level. Deeper insights into these mechanisms will provide both theoretical foundations and practical strategies for enhancing carotenoid accumulation and stress tolerance in crops through molecular design.

Promoter Regions, Genetic↗
PubMed1976

Codon-dependent rearrangement of the three-dimensional structure of phenylalanine tRNA, exposing the T-psi-C-G sequence for binding to the 50S ribosomal subunit.

Codon-anticodon interaction induces an allosteric rearrangement of the three-dimensional structure of Phe-tRNAPhe that exposes the T-psi-C-G sequence for binding to the C-G-A-A sequence of the 5S rRNA within the 50S ribosomal subunit. The conformational change in the tRNAPhe structure was followed by the binding of C-G-[3H]A-[3H]A to the T-psi-C-G sequence, as measured by equilibrium dialysis at 10 mM Mg2+. C-G-A-A (14 pmol) was bound to tRNAPhe in the complete system containing elongation factor Tu-GTP-Phe-tRNA-(uridylyl-3',5')7-uridine-30S ribosomes (100 pmol). At a Mg2+ concentration lower than 5 mM the rearrangement was dependent on elongation factor-Tu, whereas GTP could be replaced by guanylyl imidodiphosphonate. In the absence of elongation factor-Tu-GTP a sigmoidal C-G-A-A binding curve with respect to Mg2+ concentration was obtained, showing half-saturation at 6 mM Mg2+. To achieve the change in the tRNAPhe structure in the absence of 30S ribosomes, a twofold higher concentration of (uridylyl-3',5')7-uridine had to be used. A sigmoidal curve was obtained again when the Mg2+ dependence of the C-G-A-A binding was followed, with 12 pmol of C-G-A-A being bound to 200 pmol of Phe-tRNA. Since T-psi-C-G exposure should influence the binding of Phe-tRNA to 70S ribosomes, Phe-tRNA binding to 70S ribosomes was examined. In the "nonenzymatic" binding (i.e., no elongation factor-Tu-GTP) of Phe-tRNA a sigmoidal Mg2+ dependence was found, whereas the "enzymatic" binding (elongation factor-Tu-GTP present) showed a hyperbolic curve. With 30S ribosomes as controls, only hyperbolic binding curves were found. The Mg2+ dependence of AA-tRNA binding thus reflects the rearrangement of the tRNA structure.

Base Sequence↗
PubMed1976

The effect of mercuric chloride intoxication on urinary psi-glutamyl transpeptidase excretion in the sheep.

The activity of the enzyme psi-glutamyl transpeptidase (psi-GT) was measured in the urine of sheep. In clinically normal animals the mean value was 6-3+/-0-6 mU/ml. In sheep with kidney damage induced by the administration of mercuric chloride there were marked increases in urinary concentrations of psi-GT, in some cases values in excess of 1000 mU/ml were recorded. This enzyme may be of value in the diagnosis of certain forms of renal disease.

Animals↗
PubMed1979

Extrachromosomal psi+ determinant suppresses nonsense mutations in yeast.

The extrachromosomal psi+ determinant in the yeast Saccharomyces cerevisiae enhanced the expression of Mendelian UAA suppressors by 6- to 10-fold. The psi+ determinant by itself is a weak UAA suppressor that caused the production of approximately 1% of the normal level of iso-1-cytochrome c in a strain containing the UAA mutation cycl-72.

Cytochrome c Group↗
PubMed1976

Preparation of qualitative standard mixtures of polychlorinated dibenzo-rho-dioxins and dibenzofurans by ultraviolet and psi-irradiation of the octachloro compounds.

High-resolution gas chromatography using an OV-17 glass capillary column and mass spectrometry were used to analyze uv-and psi-irradiated octachlorodibenzo-rho-dioxin and octachlorodibenzofuran. Under the conditions investigated, dechlorination of these compounds to lower chlorinated dibenzo-rho-dioxins and dibenzofurans appears to be the major reaction pathway. The resulting mixtures of penta-, hexa-and heptachloro compounds can be used as easily and safely prepared qualitative reference samples to determine gas chromatographic, mass spectrometric and other properties of individual components for which pure standards are not available.

Benzofurans↗