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131.
Abstract Highly purified preparations of inner, i.e. cytoplasmic and intracytoplasmic, membranes and outer membranes were isolated from Nitrobacter hamburgensis strain X14 by sucrose density-gradient centrifugation of cell-free extracts. The two membrane fractions differed markedly in morphology, density, and protein composition as determined by polyacrylamide gel electrophoresis. The inner membrane fraction was enriched in NADH oxidase and nitrite oxidase activity. It contained four major protein bands of apparent M r s of 28 000, 32 000, 70 000, and 116000. The outer membrane fraction was characterized by the presence of 2-keto-3-deoxyoctonate and contained two major proteins of apparent M r s of 13 000 and 50 000. There was no evidence for differences between cytoplasmic and intracytoplasmic membranes. 相似文献
132.
Assessment of a model for intron RNA secondary structure relevant to RNA self-splicing--a review 总被引:36,自引:0,他引:36
A widespread class of introns is characterized by a particular RNA secondary structure, based upon four conserved nucleotide sequences. Among such "class I" introns are found the majority of introns in fungal mitochondrial genes and the self-splicing intron of the large ribosomal RNA of several species of Tetrahymena. A model of the RNA secondary structure, which must underlie the self-splicing activity, is here evaluated in the light of data on 16 further introns. The main body or "core structure" of the intron always consists of the base-paired regions P3 to P9 with the associated single-stranded loops, with P2 present also in most cases. Two minority sub-classes of core structure occur, one of which is typical of introns in fungal ribosomal RNA. Introns in which the core structure is close to the 5' splice site all have an internal guide sequence (IGS) which can pair with exon sequences adjacent to the 5' and 3' splice sites to align them precisely, as proposed by Davies et al. [Nature 300 (1982) 719-724]. In these cases, the internal guide model allows us to predict correctly the exact location of splice sites. All other introns probably use other mechanisms of alignment. This analysis provides strong support for the RNA splicing model which we have developed. 相似文献
133.
SYNOPSIS Triplet conjugants of Paramecium caudatum which appeared naturally in mating mixtures and those of Paramecium multimicronucleatum which were produced by conjugation-inducing chemicals were isolated. Triplet conjugants lasting for more than 3 h were stained to examine macronuclear events. In P. caudatum , only 2 triplets among 182 (1%) contained macronuclear fragmentation in all 3 members. The most frequently occurring triplets (79%) were those producing 1 cell without and 2 cells with macronuclear fragments. There were also triplets (17%) producing 1 cell with, and 2 without macronuclear fragments, and some (3%) with 3 cells that contained no fragments. The length of persistence of the triplet was not responsible for the occurrence of macronuclear fragmentation in the 3rd cell of the triplet. In P. multimicronucleatum , the same 4 classes of triplets occurred, but the most frequently occurring class was that consisting of 3 cells (91%) with macronuclear fragments. Induction of nearly 100% of triplets with 3 such cells was possible by isolating the triplets' from a culture which was treated chemically at about 24 h after the last feeding. Treatment with chemicals in starved cultures resulted in triplets with incompletely fragmented or nonfragmented macronuclei. Further, in P. multimicronucleatum , chemicallyinduced triplets involving only holdfast pairs to which the 3rd cells were uniting often produced 3 cells with fragmented macronuclei. 相似文献
134.
Lack of repair of ultraviolet light damage in Mycoplasma gallisepticum 总被引:10,自引:0,他引:10
Molecules with single-stranded tails (rolling circles) were isolated as replicating intermediates in G4 progeny single-stranded DNA synthesis. Lysates from infected cells harvested late in infection during single-stranded DNA synthesis were not deproteinised but analysed directly in caesium chloride and propidium diiodide gradients. The gradient fractionated them on the basis of tail length. If the lysates were first deproteinised however, the tailed replicative intermediates banded as a peak at a density just greater than that of replicative form II DNA (RFII) and did not spread down the gradient. The origin of synthesis of the viral strand tail was mapped by electron microscopy as 55 to 60% away from the single EcoRI cleavage site. Termination molecules finishing a round of viral strand DNA synthesis have been identified as molecules consisting of a closed single-stranded DNA circle attached by a very small region to the parent double-stranded DNA circle. 相似文献
135.
The conversion of both parental- and progeny-nascent open circular M13 RF DNA into covalently closed RF I is drastically reduced in an mutant deficient in the 5′ → 3′ exonuclease associated with DNA polymerase I. The nascent progeny RF DNA also contains a significant proportion of fragments of smaller than unit length. 相似文献
136.
Leaves of greenhouse grown grasses had free protein amino acid contents of generally less than 5 % total amino acids, while field collected grasses averaged 14.7 % free protein amino acid contents. Taxonomic patterns are detectable in the total leaf amino acid profiles of grasses from both sources, those of pooids being distinguishable from those of chloridoids and panicoids, and those of danthonioids showing an intermediate pattern. Leaf profiles of Oryza, Stipeae, and Ehrharteae resemble one another, and are more like those of pooids than those of panicoids. Variations in Thr and Leu are apparently associated with differences in photosynthetic pathway. Grass leaves are generally low in total amino acid contents (2.2 ? 1.0 g % fr. wt), with Ile, Val and Met + Cys identified as the limiting essential amino acids. However, the nutritional ‘chemical scores’ of grass leaf proteins are high (75 %, based on the WHO scoring pattern). 相似文献
137.
138.
3-(2-Carboxyethyl)thymine (3-CET) was synthesized from β-propiolactone (BPL) and dThd5′P at pH 9.0–9.5 via the intermediate 3-(2-carboxyethyl)thymidine-5′-monophosphoric acid (3-CEdThd5′P). 3-CEdThd5′P was converted to 3-CET by hydrolysis in 1.5 N HCl at 100°C for 2 h. The structure of 3-CET was assigned on the basis of UV spectra, electron impact (EI) and isobutane chemical ionization mass spectra and the EI mass spectrum of a trimethylsilyl derivative of 3-CET. BPL was reacted in vitro with calf thymus DNA at pH 7.5. 100 A units of BPL-reacted DNA yielded, following perchloric acid hydrolysis and preparative paper chromatography, 3 A units of 3-CET. Reaction of BPL with the phosphodiester thymidylyl-(3′-5′)thymidine gave 3-(2-carboxyethyl)thymidylyl-(3′-5′)-3-(2-carboxyethyl)thymidine (~3%). Phosphotriester formation was not detected. 相似文献
139.
140.
E. B. Sansone A. M. Losikoff W. B. Lebherz III J. A. Poiley 《In vitro cellular & developmental biology. Plant》1981,17(9):811-815
Summary To estimate worker exposures to, and environmental contamination from, test chemicals and organic solvents used in an in vitro
assay to assess the carcinogenic potential of chemicals, sodium fluorescein, a noncarcinogenic fluorescent material, was dissolved
in tissue culture medium used to maintain early passage hamster embryo cells. Personal and environmental samples were taken
over a 14-d period. The assay was performed according to standard procedures in a ventilated glove box or laminar flow safety
cabinet. Considerably more than 99% of the chemical contamination found was recovered from the interiors of the glove box
and hood and from disposable equipment. Contamination outside the containment units (less than 1 μg) resulted from intralaboratory
transport of chemicals, treated cultures, and contaminated equipment. We conclude that the standard operating practices and
procedures provided adequate safeguards for personnel and the environment.
Research sponsored by the National Cancer Institute under Contract N01-CO-75380, with Litton Bionetics, Inc. 相似文献