Role of SSB protein in RecA promoted branch migration reactions

Summary The RecA protein ofEscherichia coli is essential for genetic recombination and postreplicational repair of DNA. In vitro, RecA protein promotes strand transfer reactions between full length linear duplex and single stranded circular DNA of X174 to form heteroduplex replicative form II-like structures (Cox and Lehman 1981a). In a similar way, it transfers one strand of a short duplex restriction fragment to a single stranded circle. Both reactions require RecA and single strand binding protein (SSB) in amounts sufficient to saturate the ssDNA. The rate and extent of strand transfer is enhanced considerably when SSB is added after preincubation of the DNA with RecA protein. In contrast, SSB protein is not required for RecA protein catalysed reciprocal strand exchanges between regions of duplex DNA. These results indicate that while SSB is necessary for efficient transfer between linear duplex and ssDNA to form a single heteroduplex, it is not required for branch migration reactions between duplex molecules that form two heteroduplexes.Abbreviations SSB single strand binding protein - ssDNA single stranded DNA - X phage X174 - bp base pairs - ATP[S] adenosine 5-O-(gamma-thiotriphosphate)     

Muscarinic cholinergic and preganglionic physiological stimulation increase cyclic GMP levels in guinea-pig superior cervical ganglia.

Abstract— Incubation of guinea-pig superior cervical ganglia in 500μ4mUm -carbachol for 2min increased cyclic GMP levels 530% over control values. The increase was blocked by prior incubation in 300μm atropine. No increase in cyclic GMP levels after incubation in 100 μm -l -norepinephrine was observed. Preganglionic physiological stimulation for 8 min at 10 Hz increased cyclic GMP levels 180% over control values. We conclude that both muscarinic cholinergic and preganglionic physiological stimulation increase cyclic GMP levels in guinea pig superior cervical ganglia, while norepinephrine has no effect.     

Effect of incubation temperature on the frequency of sister chromatid exchanges in Bloom's syndrome lymphocytes

Summary The effect of incubation temperature on the frequency of sister chromatid exchange (SCE) has been studied in blood cultures from three Bloom's syndrome (BS) patients, three controls, and three BS heterozygotes. All cell types show slight increases of SCE at 39°C while at 35°C and 32°C, SCE is reduced considerably in BS and slightly increased in normal cells. Prolonging lymphocyte culture to 140 h and adding BUdR for the last two S periods causes a similar decrease in the percentage of SCE in normal and BS cells but, while the latter show a further reduction if they are incubated at 32°C during BUdR labelling, the normal cells show an increase. Therefore, BS and control lymphocytes respond similarly to changes in incubation time and differently to changes in incubation temperature. The possibility that the discrepant behaviour of the BS and control cultures may be due to different growth kinetics of their B and T lymphocytes has been discussed but considered unlikely. Since low temperature lengthens the cell cycle, it has been suggested that our findings and those published by others on co-cultivation experiments (except those of Tice et al. 1978) can be explained by assuming that slow growth reduces SCE in BS cells. This, and unpublished observations (Giannelli et al. 1981), suggest that some imbalance in the factors responsible for DNA replication may exist in BS and possibly account for the high level of SCE.     

Non-random X-chromosome expression early in mouse development

We have used a sensitive electrophoretic technique for estimating the activity, or ratio, of two allozymes of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1), in order to investigate the randomness of X-chromosome expression in the derivatives of the three primary cell lineages of the early mouse conceptus. The maternally derived Pgk-1 allele is preferentially expressed in the derivatives of the primitive endoderm and trophectoderm lineages at 6 1/2 days post coitum in Pgk-1^a/Pgk-1^b heterozygous conceptuses, and in the one informative 5 1/2-day heterozygous conceptus analysed. This evidence for preferential expression of the maternally derived X chromosome (X^m), so soon after the time of X-chromosome inactivation, favors the possibility that the preferential expression of X^m is a consequence of primary non-random X-chromosome inactivation, rather than a secondary selection phenomenon. The majority of embryos analysed at 4 1/2 and 5 1/2 days pc produced only a single PGK-1 band, corresponding to the allozyme produced by the Pgk-1 allele on X^m, although 50% of these embryos should have been heterozygous females. Possible explanations are discussed.     

Virus-like particles in the brown algaStreblonema

Summary Ultrastructural examination ofStreblonema sp. revealed icosahedral virus-like particles (135–150 nm) throughout the cytoplasm of vegetative cells. The densely packed particles consist of an osmiophilic coat around a fibrillar core. Most cytoplasmic organelles are excluded from the regions where the particles are extremely abundant, but no degeneration of plastids, mitochondria or dictyosomes is evident. The virogenic stroma contains many ribosomes and fibers possibly representing DNA strands remaining from the lysed nucleus. No decrease in vigor seemed to be associated with the presence of the particles.     

Comparison of microbial counts on beef carcasses by using the moist-swab contact method and secondary tissue removal technique.

When a tissue removal rinse technique was compared to the moist-swab contact method, significantly greater numbers of bacteria were recovered from beef carcasses, especially when the flora exceeded log10 4.5/6.45 cm2. Secondary treatment of the removed surface tissue by blending resulted in a significantly greater number of bacteria being recovered than when the same sample was swabbed and/or rinsed. Data indicate that blending of the carcass surface tissue provides a more representative value of the true microbial flora.     

The annual lipid cycle and feeding behavior of Alaskan redpolls

Summary Total lipids were extracted from 161 redpolls (Acanthis spp.) collected each month of the year from October 1962 to September 1963, in interior Alaska. A lipid index (Weight of ether extract x100/live body weight) was calculated for each sample. Lipids were also extracted from sections of pectoral muscle, livers and hearts representing each month.Body weight and lipid index were significantly positively correlated being highest in January and lowest in September. Total lipid content was significantly inversely correlated with air temperature; the high autumn and spring pre-migratory lipid peaks of migratory species were only weakly expressed in the redpolls. Liver lipid showed a significant annual variation being highest in December and lowest in August, while lipid from heart and pectoral muscle did not vary seasonally.Five birds were held in captivity during spring and summer at a constant temperature of 22°C. Food consumption was 5.1 g/day or 22.4 kcal. The caloric value of the most extensively utilized natural food, birch seed (Betula papyrifera), was determined (5.4–5.5 kcal/g dry wt). When esophageal diverticulae are full (2.0 g wet wt) of birch seeds, the resulting energy yield may sustain an individual for only a fraction of a 24 h winter day in contrast to other arctic herbivores (e.g. ptarmigan, Lagopus sp.) in which a full crop may suffice for the full 24 h period.     

Identification of protein X of Escherichia coli as the recA+/tif+ gene product.

Summary Protein X, molecular weight 40,000, has been separated from the other proteins of E. coliby a two-dimensional gel electrophoretic technique which separates proteins according to isoelectric point (pI) in the firstdimension and according to molecular weight in the second. When protein X is induced in wild-type cells by mitomycin C treatmentit has a pI6.0. However, when protein X is induced in a tif-1 mutant, either by temperatureshift-up to 42° or by mitomycin C treatment at 30°, it has a pI6.2. The low level of protein X which is present inuninduced tif mutants at 30° also has a pI6.2. These results suggest thattif-1 is a mis-sense mutation in the gene coding for protein X. Since transduction andcomplementation studies indicate that tif-1 is a mutation of therecA ⁺ gene (Castellazzi, Morand, George and Buttin, 1977) it follows that protein X is the recA ⁺ gene product.A model has been formulated to account for the relationship between protein X synthesis and the recA ⁺ and lexA ⁺ genes. In this model, a repressor coded by lexA ⁺ binds to the operator of the recA ⁺ gene from whence it can normally only be removed by the combined action of an inducer and protein X, the recA ⁺ product. Thus, protein X controls its own synthesis. The tif-1 mutation leads to a temperature sensitive form of protein X which, at 42°, can spontaneously remove the repressor without the intervention of the inducer.