Most of the homoeologous pairing at metaphase I in wheat-rye hybrids is not chiasmatic

The use of telomeric C-bands in wheat-rye hybrids has made it possible to distinguish three types of wheat-wheat (1B^L) and wheat-rye associations (a, end-to-end extremely distal; b, end-to-ed distal; and c, interstitial) between homoeologous chromosomes at different metaphase I stages (early, middle and late) and also to estimate the actual recombination frequencies for such associations at anaphase I. There was a decrease of the a and b association frequencies during the different metaphase I stages, whereas the c type remained without variation in all stages. A good fit between the frequencies of c associations at metaphase I and the number of recombinant chromosomes at anaphase I, assuming a maximum of one chiasma per bond, was found; however, there was no correspondence between metaphase I and anaphase I data when all associations (a + b + c) were considered. In addition, rye-rye homologous pairing was observed at metaphase I, but no evidence for rye-rye recombination was found at anaphase I. The results indicate that most of end-to-end (a and b) homoeologous and nonhomologous associations are actually nonchiasmatic and are a remnant of prophase pairing.     

AN ANALYSIS OF HETEROCHROMATIN IN MAIZE ROOT TIPS

The B chromosomes of maize are condensed in appearance during interphase and are relatively inert genetically; therefore they fulfill the definition of heterochromatin. This heterochromatin was studied in root meristem cells by radioautography following administration of tritiated thymidine and cytidine, and was found to behave in a characteristic way, i.e. it showed asynchronous DNA synthesis and very low, if any, RNA synthesis. A cytochemical comparison of normal maize nuclei with nuclei from isogenic maize stock containing approximately 15–20 B-chromosomes in addition to the normal complement has revealed the following: (a) the DNA and histone contents are greater in nuclei with B chromosomes; (b) the proportion of DNA to histone is identical with that of nuclei containing only normal chromosomes; (c) the amount of nonhistone protein in proportion to DNA in interphase is less in nuclei with B chromosomes than in normal nuclei. In condensed B chromosomes the ratio of nonhistone protein to DNA is similar to that in other condensed chromatin, such as metaphase chromosomes and degenerating nuclei. The B chromosomes appear to have no effect on nucleolar RNA and protein. Replication of B chromosomes is precisely controlled and is comparable to that of the ordinary chromosomes not only in synthesis for mitosis but also in formation of polyploid nuclei of root cap and protoxylem cells.     

Oxidation-reduction potentials of respiratory chain components in ThiobacillusA2

(1) Cells of ThiobacillusA₂ grown chemoautotrophically on thiosulfate or heterotrophically on succinate with oxygen contained b-, c-, o-, a- and a₃-type cytochromes. The amount of cytochrome per mg of cell protein was much greater in thiosulfate-grown cells and differences in the relative concentrations of cytochromes were observed for the different growth conditions. (2) The half-reduction potentials at pH 7.0 (E_m,7.0) and spectral maxima of c-, b-, a- and a₃-type cytochromes were similar in cells grown aerobically with thiosulfate or with succinate as the growth substrate. (3) The half-reduction potential of the ‘invisible’, or high-potential copper, as determined from the potentiometric behavior of the carbon monoxide-reduced cytochrome a₃ complex at pH 8.0, was 365 mV. (4) Reducing equivalents from thiosulfate appear to enter the respiratory chain at the cytochrome c level; however, studies in cell-free extracts were limited due to a loss in respiratory activity with thiosulfate as a substrate upon cell disruption.     

AN ANALYSIS OF DNA LOSS AND SYNTHESIS IN THE RAT ADRENAL MEDULLA NUCLEI UPON COLD STIMULATION

The peculiar changes previously observed in DNA content of rat adrenal medulla cell nuclei upon intermittent cold exposure (15 hr at +4°C followed by 9 hr at room temperature) have been further studied with the aid of Feulgen histophotometry and H₃-thymidine radioautography. The amount of DNA decreases progressively with increasing length of cold exposure until 300 hr (-32%). Later a rapid change takes place, whereby DNA content per nucleus returns to values which are slightly, but consistently lower than normal. At termination of a period of cumulative exposure to cold, an analysis of a whole-day experimental cycle shows that the DNA decrease is due to loss of DNA during cold exposure and that DNA synthesis occurs upon return to room temperature. The balance between these two processes can be divided into three stages: (a) loss of DNA up to 300 hr of cumulative cold exposure; (b) marked increase in DNA by 350 hr; (c) oscillation around zero or slightly negative at 400 hr and beyond. These variations are due to: (1) the extension of DNA synthesis into the period of cold exposure as clearly demonstrated by radioautography (stage b), and (2) a later still greater DNA loss (stage c) which partly offsets the increased synthesis. A complex pattern of adaptation of the adrenal medulla cells, as regards DNA content, to the repetitive cold stimulus is thus demonstrated.     

Radiation-stimulated DNA synthesis in cultured mammalian cells

A type of DNA synthesis in mammalian cells that is stimulated by ultraviolet light has been studied by means of radioautography and density gradient centrifugation. The characteristics of this synthesis are: (a) it is not semiconservative; (b) it is enhanced by the presence of 5-bromodeoxyuridine in the DNA molecule; (c) the degree of stimulation is dose dependent; (d) there is less variability in the rate of incorporation of H³-thymidine during this synthesis than during normal DNA synthesis; (e) it occurs in cells that are not in the normal DNA synthesis phase (G₁ and G₂ cells). This kind of synthesis has been found in cultured cell lines from five different species; however, in some strains, the presence of bromouracil in the DNA is required before it can be demonstrated by radioautography.     

MACROMOLECULAR SYNTHESES RELATED TO THE REPRODUCTIVE CYST OF TETRAHYMENA PATULA

Macromolecular syntheses in encysted Tetrahymena patula were studied using Feulgen fluorescence cytophotometry, autoradiography, and inhibitors of RNA and protein synthesis. Cycloheximide significantly depressed protein synthesis and D-actinomycin effectively blocked RNA synthesis. Under these conditions, the cells within the cyst were unable to divide. Both cytophotometric measurements and autoradiographic data with tritiated thymidine show that DNA synthesis does not occur during the encystment divisions. Excysted cells placed in nutrient broth medium showed a prolonged generation time after the first cell growth cycle, and by the third generation the mean DNA content per cell was almost triple that of starved excysted cells. These findings indicate that (a) the encystment divisions require RNA and protein synthesis, which are apparently effected through turnover, (b) the encystment division cycles occur in the absence of DNA synthesis, and (c) excysted cells placed in culture medium may go through more than one DNA replication per cell cycle.     

PHYSICAL CHEMICAL STUDIES ON THE SPECIFIC INTERACTION OF AN ACRIFLAVINE-PHOSPHOTUNGSTIC ACID COMPLEX WITH DOUBLE-STRANDED NUCLEIC ACIDS

The detailed definition of the structure of DNA in chromosomes and in interphase chromatin is important for correlating the structure of the genetic material with various states of physiological activity. A general approach to developing specific reagents for a variety of such studies in solution and in tissues is to combine a chemically specific organic cation with the electron-opaque phosphotungstic acid (PTA) molecule. The reagent described in this paper was made from the interaction of acriflavine and phosphotungstic acid. The acriflavine-PTA complex (a) displays some unique absorption and fluorescence properties, (b) binds specifically to DNA and RNA by intercalation of the acriflavine moiety, and (c) is electron opaque. In addition, it binds to double-stranded synthetic polynucleotides, but not to a variety of proteins, nucleoproteins, or polysaccharides.     

Synthesis and antitumor activity of novel 1-substituted phenyl 3-(2-oxo-1,3,4-oxadiazol-5-yl) β-carbolines and their Mannich bases

A series of novel 1-(substituted phenyl)-3-(2-oxo-1,3,4-oxadiazol-5-yl) β-carbolines (4a–e) and the corresponding Mannich bases 5–9(a–c) were synthesized and evaluated for their in vitro antitumor activity against seven human cancer cell lines. Compounds of 4a–e series showed a broad spectrum of antitumor activity, with GI₅₀ values lower than 15 μM for five cell lines. The derivative 4b, having the N,N-dimethylaminophenyl group at C-1, displayed the highest activity with GI₅₀ in the range of 0.67–3.20 μM. A high selectivity and potent activity were observed for some Mannich bases, particularly towards resistant ovarian (NCI-ADR/RES) cell lines (5a, 5b, 6a, 6c and 9b), and ovarian (OVCAR-03) cell lines (5b, 6a, 6c, 9a, 9b and 9c). In addition, the interaction of compound 4b with DNA was investigated by using UV and fluorescence spectroscopic analysis. These studies indicated that 4b interact with ctDNA by intercalation binding.     

NUCLEOLAR-DERIVED RIBONUCLEIC ACID IN CHROMOSOMES, NUCLEAR SAP, AND CYTOPLASM OF CHIRONOMUS TENTANS SALIVARY GLAND CELLS

The distribution of monodisperse high molecular weight RNA (38, 30, 28, 23, and 18S RNA) was studied in the salivary gland cells of Chironomus tentans. RNA labeled in vitro and in vivo with tritiated cytidine and uridine was isolated from microdissected nucleoli, chromosomes, nuclear sap, and cytoplasm and analyzed by electrophoresis on agarose-acrylamide composite gels. As shown earlier, the nucleoli contain labeled 38, 30, and 23S RNA. In the chromosomes, labeled 18S RNA was found in addition to the 30 and 23S RNA previously reported. The nuclear sap contains labeled 30 and 18S RNA, and the cytoplasm labeled 28 and 18S RNA. On the basis of the present and earlier analyses, it was concluded that the chromosomal monodisperse high molecular weight RNA fractions (a) show a genuine chromosomal localization and are not due to unspecific contamination, (b) are not artefacts caused by in vitro conditions, but are present also in vivo, and (c) are very likely related to nucleolar and cytoplasmic (pre)ribosomal RNA. The 30 and 23S RNA components are likely to be precursors to 28 and 18S ribosomal RNA. The order of appearance of the monodisperse high molecular weight RNA fractions in the nucleus is in turn and order: (a) nucleolus, (b) chromosomes, and (c) nuclear sap. Since both 23 and 18S RNA are present in the chromosomes, the conversion to 18S RNA may take place there. On the other hand, 30S RNA is only found in the nucleus while 28S RNA can only be detected in the cytoplasm, suggesting that this conversion takes place in connection with the exit of the molecule from the nucleus.     

Damage by Visible Light to the Acridine Orange-DNA Complex

Salmon DNA has been irradiated with visible light in the presence of acridine orange. If the dye is bound to the DNA, there results: (a) a decrease in sedimentation coefficient, (b) a lowering of viscosity, and (c) a decrease in the thermal denaturation temperature. CsCl banding experiments show that the first two effects reflect depolymerization of the DNA. Depolymerization apparently occurs by single-strand scission although some double-strand scission is not excluded. The destabilization of secondary structure results probably from chemical attack on the components of the individual strands.     

Changes in cytochrome contents and respiratory activity of Bacillus cereus Strain T during germination, vegetative growth and sporulation

Vegetative cells of Bacillus cereus Strain T contain cytochromeb-562, a minor b-type component, in addition to known components,cytochrome a+a₃, cytochrome b-557 and cytochrome c-551. Also,the spores contain low but definite amounts of cytochromes b-562and c-551, which were oxidized when the spores were shaken withair. Contents of cytochromes a, b and c per cell and per cellnitrogen, and the activity of glucose oxidation increased duringspore germination and elongation. During the stage precedingfirst cell division, cytochrome contents per cell increasedin parallel with the increase of cell nitrogen, while the activityof glucose oxidation decreased. During early exponential growth,the content of cytochrome b per cell nitrogen and respiratoryactivity with glucose again increased. When cells entered thesporulation stage, characterized by structural changes insidethe cells, the activity of glucose oxidation began to decrease,while that of acetate or succinate oxidation started to increase.During the sporulation process, the contents of the three cytochromecomponents continued to increase and reached the highest levelin cells containing completed spores, but the activity of respirationwith endogenous or added substrates was negligible in thesecells. (Received November 10, 1975; )     

基因倍增和脊椎动物起源

有机体基因复制导致基因复杂性增加及其和脊椎动物起源的关系已经成为进化生物学研究的热点。20世纪70年代由Ohno提出后经Holland等修正的原始脊索动物经两轮基因组复制产生脊椎动物的假设目前已被广泛接受。脊椎动物起源和进化过程中发生过两轮基因组复制的主要证据有三点：（1）据估计脊椎动物基因组内编码基因数目大约相当于果蝇、海鞘等无脊椎动物的4倍;原口动物如果蝇和后口动物如头索动物文昌鱼的基因组大都只有单拷贝的基因,而脊椎动物的基因组则通常有4个同属于一个家族的基因。（2）无脊椎动物如节肢动物、海胆和头索动物文昌鱼都只有一个Hox基因簇,而脊椎动物除鱼类外,有7个具有Hox基因簇,其余都具有4个Hox基因簇。（3）基因作图证明,不但在鱼类和哺乳动物染色体广大片段上基因顺序相似,而且有证据显示哺乳动物基因组不同染色体之间存在相似性。据认为第一次基因倍增发生在脊椎动物与头索动物分开之后,第二次基因倍增发生在有颌类脊椎动物和无颌类脊椎动物分开以后。但是,基因是逐个发生倍增,还是通过基因组内某些DNA片段抑或整个基因组的加倍而实现的,目前还颇有争议。     

Depolarization of the intrinsic and extrinsic fluorescence of pepsinogen and pepsin

1. The effects on the intrinsic tryptophan emission anisotropy of pepsin and pepsinogen solutions produced by (a) changes in temperature, (b) increases in viscosity with added glycerol at constant temperature and (c) decreases in lifetime through collisional quenching by potassium iodide were measured at several excitation wavelengths. The rotational-relaxation times calculated from results provided by method (b) approximate to the theoretical values for the two proteins, on taking hydration and shape factors into account, on the basis of random orientation of the tryptophan groups within the macromolecules. Differences between the results provided by methods (b) and (c) are attributable to inter-tryptophan resonance-energy-transfer depolarization, and the anomalous values recorded in method (a) can be attributed to the temperature-dependence of the limiting anisotropies. 2. Two different monomeric conjugates of pepsin, each containing one extrinsic fluorescent group per macromolecule, gave widely different relaxation times. This difference may arise from a specific orientation of the emission dipole in the enzyme. In active-site-labelled pepsin (1-dimethylaminonaphthalene-5-sulphonylphenylalanine–pepsin) this orientation would be approximately parallel to the symmetry axis of the equivalent ellipsoid, whereas in the other conjugate (1-dimethylaminonaphthalene-5-sulphonyl-pepsin) the orientation may be roughly normal to this direction, or some independent rotation of parts of the protein molecule is possible.     

Analysis of the Light-harvesting Pigment-Protein Complex of Wild Type and a Chlorophyll-b-less Mutant of Barley

we have compared chloroplast lamellae isolated from a chlorophyll-b-less mutant and wild type barley (Hordeum vulgare). The results demonstrate that: (a) one of the two major polypeptides comprising the lightharvesting complex (LHC) is present in the chlorophyll-b-less mutant; (b) higher cation concentrations are required to maintain grana stacks in the mutant; and (c) cation effects on excitation energy distribution are present in the chlorophyll-b-less mutant but are reduced in amount and are dependent on higher concentrations of cations.     

Biosynthesis of Photosystem II Reaction Centers, Antenna and Plastoquinone Pool in Greening Cells of Cyanidium caldarium Mutant III-C

Dark-grown etiolated cells of Cyanidium caldarium mutant III-C lacking ≥99% of their normal chlorophyll content and inactive for photosynthesis were greened in continuous light. Measurements of oxygen evolution and fluorescence kinetics indicate that during greening: (a) the photosystem II (PSII) antenna containing between 30 and 40 chlorophyll a per center undergoes little change in size from 5% of the centers synthesized per cell to fully active cells; (b) energy transfer between PSII centers appears very early in the greening process; (c) the plastoquinone pool size per PSII center (about 14 equivalents) does not vary during greening and has already attained full size after synthesis of only 13% of the full complement of centers.     

Variations in Several Responses of HeLa Cells to X-Irradiation during the Division Cycle

Several responses of synchronized populations of HeLa S3 cells were measured after irradiation with 220 kev x-rays at selected times during the division cycle. (1) Survival (colony-forming ability) is maximal when cells are irradiated in the early post-mitotic (G₁) and the pre-mitotic (G₂) phases of the cycle, and minimal in the mitotic (M) and late G₁ or early DNA synthetic (S) phases. (2) Markedly different growth patterns result from irradiation in different phases: (a) Prolongation of interphase (division delay) is minimal when cells are irradiated early in G₁ and rises progressively through the remainder of the cycle. (b) Cells irradiated while in mitosis are not delayed in that division, but the succeeding division is delayed. (c) Persistence of cells as metabolizing entities does not depend on the phase of the division cycle in which they are irradiated. (3) Characteristic perturbations of the normal DNA synthetic cycle occur: (a) Cells irradiated in M suffer a small delay in the onset of S, a slight prolongation of S, and a slight depression in the rate of DNA synthesis; the major delay occurs in G₂. (b) Cells irradiated in G₁ show no delay in the onset of S, and essentially no alteration in the duration or rate of DNA synthesis; G₂ delay is minimal. (c) Cells irradiated in S suffer an appreciable S prolongation and a decreased rate of DNA synthesis; G₂ delay is shorter than S delay.     

Integration of Deoxyribonuclease-Treated DNA in Bacillus subtilis Transformation

Normal preparations of B. subtilis DNA have weight average native molecular weights of 10 to 30 x 10⁶. For any given preparation the upper and lower 95% size limits may differ by a factor of ten or more. Single-stranded molecular weights indicate an average of 1 to 4 breaks per single strand of the native DNA. The reduction in transforming activity and viscosity following DNAase I digestion can be accounted for by a direct relationship between the transforming activity of a DNA and its single-stranded molecular weight. Uptake studies with DNAase I treated heavy (²H¹⁵N ³H) DNA show that single strand breaks inhibit integration less than transformation. A provisional estimate of the size of the integrated region based on correlating the single strand size of the donor-recipient complex with the donor-recipient density differences following alkali denaturation came to 1530 nucleotides. Using a competent, nonleaky thymine-requiring strain of B. subtilis grown in 5-BU medium before and after transformation, it was shown that (a) No detectable amount of DNA synthesis is necessary for the initial stages of integration, (b) Cells which have recently been replicating DNA are not competent. (c) Cells containing donor DNA show a lag in DNA replication following transformation, (d) When donor DNA is replicated it initially appears in a density region between light and hybrid. This indicates that it includes the transition point formed at the time of reinitiation of DNA synthesis in the presence of 5-BU following transformation. A model is proposed in which donor DNA is integrated at the stationary growing point of the competent cell, which is in a state of suspended DNA synthesis.     

Electroretinogram Characteristics and the Spectral Mechanisms of the Median Ocellus and the Lateral Eye in Limulus polyphemus

Electrical responses (ERG) to light flashes of various wavelengths and energies were obtained from the dorsal median ocellus and lateral compound eye of Limulus under dark and chromatic light adaptation. Spectral mechanisms were studied by analyzing (a) response waveforms, e.g. response area, rise, and fall times as functions of amplitude, (b) slopes of amplitude-energy functions, and (c) spectral sensitivity functions obtained by the criterion amplitude method. The data for a single spectral mechanism in the lateral eye are (a) response waveforms independent of wavelength, (b) same slope for response-energy functions at all wavelengths, (c) a spectral sensitivity function with a single maximum near 520 mµ, and (d) spectral sensitivity invariance in chromatic adaptation experiments. The data for two spectral mechanisms in the median ocellus are (a) two waveform characteristics depending on wavelength, (b) slopes of response-energy functions steeper for short than for long wavelengths, (c) two spectral sensitivity peaks (360 and 530–535 mµ) when dark-adapted, and (d) selective depression of either spectral sensitivity peak by appropriate chromatic adaptation. The ocellus is 200–320 times more sensitive to UV than to visible light. Both UV and green spectral sensitivity curves agree with Dartnall's nomogram. The hypothesis is favored that the ocellus contains two visual pigments each in a different type of receptor, rather than (a) various absorption bands of a single visual pigment, (b) single visual pigment and a chromatic mask, or (c) fluorescence. With long duration light stimuli a steady-state level followed the transient peak in the ERG from both types of eyes.     

CONSTANCY OF DNA CONTENT IN ADRENAL MEDULLA NUCLEI OF COLD-TREATED RATS

Reports of changes in DNA content of certain types of cells following exposure to conditions of stress has led to the suggestion that two kinds of DNA may be present. One is genetic DNA, and the other is called "metabolic" DNA. In a further attempt to investigate the possibility of this phenomenon, determinations of DNA content were made on Feulgen-stained nuclei of adrenal glands and kidneys in cold-treated rats. Feulgen-stained nuclei were measured by two-wavelength microspectrophotometry. Particular attention was given to the handling of the smears in hydrolysis and staining. Mean values of Feulgen-DNA contents in a total of 720 nuclei demonstrated (a) a constancy of DNA content within 2% in individual nuclei both in adrenal medulla and kidney cortex, (b) no more than an average of 2% difference in DNA content between control and experimental nuclei, and (c) no more than an average of 1.5% difference in DNA content between normal kidney cortex nuclei and normal adrenal medulla nuclei. These results confirm the view that the more precise the measurement, the more accurately the constancy rule is obeyed. Moreover, there is no support for the concept of a metabolic DNA in the rat adrenal medulla.     

Isolation and Characterization of Bacterial Ribosomal RNA Cistrons

The DNA sequences which code for ribosomal DNA have been isolated and purified. The technique used has general application for RNA:DNA hybridization studies and enables the isolation of any gene for which sufficient gene product can be obtained. Experiments with isolated ribosomal RNA cistrons demonstrated that (a) the majority of the ribosomal cistrons are similar to one another; (b) the cistrons which are similar to one another are virtually identical to one another; (c) ribosomal cistrons of different bacterial species are closely related to one another.