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101.
The foliose red alga Gigartina papillata (C. Ag.) J. Ag. was studied in culture to determine its life history and possible relationship to the life history of Petrocelis middendorffii (Ruprecht) Kjellman. Carpospores cultured from individual female plants gave rise to either crustose Petrocelis-like plants that reproduced by tetraspores, or to another generation of foliose female (cystocarpic) plants that reproduced by carpospores. Apices cultured from blades of individual field-collected female plants produced either papillae with many procarps that developed cystocarps only when crossed with male plants, or papillae with few procarps that produced cystocarps in the absence of male plants. The results are interpreted to demonstrate that two types of life history occur in G. papillata: one, a sexual life history involving a crustose tetrasporophyte; the other, a possibly apomictic life history involving only cystocarpic plants. Hybridization experiments demonstrated, that G. papillata is interfertile with Gigartina-phase gametophytes cultured from tetraspores of P. middendorffii. Sexual plants of G. papillata are postulated to represent the naturally-occurring gametophyte of P. middendorffii in California. The possible relationships of the sexual and apomictic plants of G. papillata are discussed. 相似文献
102.
103.
Stephen C. West Era Cassuto Paul Howard-Flanders 《Molecular & general genetics : MGG》1982,186(3):333-338
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) 相似文献
104.
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. 相似文献
105.
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. 相似文献
106.
Parasporal inclusions in Bacillus sphaericus 总被引:1,自引:0,他引:1
107.
Virginia E. Papaioannou John D. West Theodor Bücher Ingrid M. Linke 《Genesis (New York, N.Y. : 2000)》1981,2(3):305-315
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-1a/Pgk-1b 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 (Xm), so soon after the time of X-chromosome inactivation, favors the possibility that the preferential expression of Xm 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 Xm, although 50% of these embryos should have been heterozygous females. Possible explanations are discussed. 相似文献
108.
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. 相似文献
109.
110.
C R Lazarus A Abu-Bakar R L West J L Oblinger 《Applied and environmental microbiology》1977,33(1):217-218
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. 相似文献