寡聚脱氧核苷酸d(G-C)_3的激光喇曼谱及其分析

用改进的固相磷酰三酯法合成了oligo-d(G-C)_3。以氩离子激光为激发光源,波长488nm.,在室温条件下,分别测定了纯化后的oligo-d(G-C)_3和其组分单体5’-dGMP和5’-dCMP的激光喇曼谱。观察到被测定的物质在300-2500cm~(-1)频率区间,各自都有其特征的谱形和喇曼峰。5’-dGMP和5’-dCMP谱中大多数特征峰在寡聚体的谱中消失,而在oligo-d(G-C)_3谱中出现了几处新的喇曼峰。经查证,峰832,851和899cm~(-1)系糖-磷酸主链的特征喇曼峰,另外几处峰与DNA的构象有关。实验结果表明oligo-d(G-C)_3在水溶液中(室温)主要以B-构象存在。     

A direct approach to the measurement of genetic variation in fish populations: applications of the polymerase chain reaction to studies of Atlantic cod, Gadus morhua L.

We used the polymerase chain reaction (PCR) and direct DNA sequencing to study genetic variation within and among populations of Atlantic cod, Gadus morhua , in the western North Atlantic. In a 307 bp region of the mitochondrial cytochrome b gene, 24 variable nucleotide positions define 24 genotypes, which differ by from one to six nucleotide substitutions. Greenland cod ( G. ogac ) differs from the most similar G. morhua genotype by an additional 12 nucleotide substitutions. Silent transitions dominate both intra- and interspecific comparisons, however four nucleotide substitutions within morhua result in amino acid replacements. Direct sequencing of DNA reveals substantially more of the genetic variation that exists within and between species than do previous indirect methods based on restriction fragment length polymorphisms, and thus has far greater potential to quantify such differences as may exist among fish stocks. Preliminary experiments also indicate that automation of DNA sequencing provides an efficient, rapid, and accurate means for detection of genetic variation in natural populations offish.     

Spawning patterns in the three-spined stickleback (Gasterosteus aculeatus L.): an evaluation by DNA fingerprinting

We analysed a random sample of 10 three-spined stickleback nests by DNA fingerprinting. DNA from the guardian male and a random subsample of LO fry per nest were probed with pYNZ 132, a human single-locus probe for VNTR-loci (variable number of tandem repeats). On average this probe produced DNA fingerprints of 12 scoreable bands. By comparing the bands present in each individual, we calculated band sharing indices (BSIs) between the guardian male and its fry. The BSls varied between 0.40 and 0.77 with an average (± S.D.) of 0.59 ± 0.09. We therefore conclude that the guardian male was the true father of the fry in all these nests. Once the paternal bands in each fry were determined, we compared the maternal bands among the fry of each nest. Based on the BSIs obtained with these comparisons, we found that one guardian male enticed three females to spawn in its nest, six enticed two females and three enticed one female.     

Analysis of a case of somatic instability in a strain of maize from India

A case of somatic instability affecting aleurone colour in a strain of maize from India with flint background was analysed. The somatic instability is localized to theC ¹ (Inhibitor) allele ofC locus on the short arm of chromosome 9. Molecular tests indicated thatAc is not present in the Indian stock and the evidence is consistent with the involvement of theEn (Spm) transposable element in the instability. The presence of theEn (Spm)-like element in the stock would suggest that these elements have been present in the maize genome for a long time. A new allele ofshrunken (sh1) gene with a somewhat unorthodox breeding behaviour is also described.     

Phage P22 helps phage MB78 to overcome blockage of DNA maturation in rifampicin-resistant host

Bacteriophage MB78, a virulent phage ofSalmonella typhimurium cannot grow in rifampicin-resistant mutant (rif-39) of the host having altered RNA polymerase. The temperate phage P22 which cannot multiply in presence of the virulent phage MB78 can, however, help MB78 to overcome replication inhibition in rif-39. The processing of concatemeric phage DNA to monomer is blocked in this nonpermissive host. Superinfection with P22 induces synthesis of at least five P22 specific polypeptides which help phage MB78 in the processing of the concatemeric DNA and maturation of phage particles.     

High-density photoautotrophic algal cultures: design, construction, and operation of a novel photobioreactor system

A photobioreactor system has been designed, constructed and implemented to achieve high photosynthetic rates in high-density photoautotrophic algal cell suspensions. This unit is designed for efficient oxygen and biomass production rates, and it also can be used for the production of secreted products. A fiber-optic based optical transmission system that is coupled to an internal light distribution system illuminates the culture volume uniformly, at light intensities of 1.7 mW/cm(2) over a specific surface area of 3.2 cm(2)/cm(3). Uniform light distribution is achieved throughout the reactor without interfering with the flow pattern required to keep the cells in suspension. An on-line ultrafiltration unit exchanges spent with fresh medium, and its use results in very high cell densities, up to 10(9) cells/mL [3% (w/v)] for eukaryotic green alga chlorella vulgaris. DNA histograms obtained form flow cytometric analysis reveal that on-line ultrafiltration influences the growth pattern. Prior to ultrafiltration the cells seem to have at a particular point in the cell cycle where they contain multiple chromosomal equivalents. Following ultrafiltration, these cells divide, and the new cells are committed to division so that cell growth resumes. The Prototype photobioreactor system was operated both in batch and in continuous mode for over 2 months. The measured oxygen production rate of 4-6 mmol/L culture h under continuous operation is consistent with the predicted performance of the unit for the provided light intensity.     

Tunicamycin inhibits the initiation of DNA synthesis stimulated by prostaglandin F2α in Swiss mouse 3T3 cells

Tunicamycin, an inhibitor of the asparagine-linked protein N-glycosylation, blocks the initiation of DNA synthesis in Swiss 3T3 cells stimulated by prostaglandin F_2α alone or with insulin. This effect is exerted only when tunicamycin is added from 0 to 8 h after stimulation and it decreases the rate of entry into S phase. Blocking of labeled sugar incorporation to proteins occurs regardless of the time of PGF_2α stimulation. In contrast tunicamicin does not inhibit protein synthesis. These results suggest that N-glycoprotein synthesis early during the prereplicative phase is an important event controlling the mitogenic action of PGF_2α     

The distribution of dissolved DNA in an oligotrophic and a eutrophic river of Southwest Florida

The distribution of dissolved DNA concentrations and some microbial variables were compared in an oligo-mesotrophic river (the Crystal River) and a phosphate-rich eutrophic river (the Alafia River) in Southwest Florida over a 15 month period. Concentrations of phosphate and nitrate in the Alafia River averaged 135 and 18.2 times the respective phosphate and nitrate concentrations of the oligo-mesotrophic Crystal River. The seasonal average dissolved DNA concentration for the Alafia River exceeded that of the Crystal River by a factor of 1.8 (8.2 g 1^–1 compared to 4.6 g 1^–1, respectively). The greatest concentrations of dissolved DNA in the Alafia River were found in areas that contained the largest populations of phytoplankton and bacteria (a reservoir formed from an abandoned phosphate mining pit and two downstream stations near the mouth of the river). Differences in dissolved DNA concentrations between these environments and more pristine environments (i.e. all Crystal River Stations and upstream Alafia River stations) were of the same order of magnitude (1.8 to 2.2-fold) as the differences in bacterial abundance and activity, but considerably less than differences in phytoplankton abundance and activity between such environments. Seasonal variations in dissolved DNA concentrations in the Crystal River corresponded to seasonal variations in microbial populations, with minimal values in January and greater values in July. In the Alafia River, lowest concentrations for dissolved DNA occurred in July during the wet season, when seasonal flooding of area of leaf litter yielded high levels of dissolved organic carbon (DOC) which were low in dissolved DNA. These results suggest that: 1) in situ planktonic activity is a greater source of dissolved DNA than allochthonous or terrestrial sources of DOC; 2) factors that control the magnitude of heterotrophic bacterial populations are more likely to control dissolved DNA levels than factors regulating autotrophic population activity and abundance; 3) differences in dissolved DNA between eutrophic and oligo-mesotrophic environments are often much smaller than the differences in nutrient concentration between such environments.     

Effect of different seasons on concentration of plasma luteinizing hormone and seminal quality vis-à-vis freezability of buffalo bulls (Bubalus bubalis)

Seasonal variations in semen quality, freezability and plasma luteinizing hormone (LH) levels were studied between summer and spring. Semen volume, density and initial sperm motility did not differ significantly between different seasons. Plasma LH decreased between summer and spring but the differences were, however, not significant. Pre-freezing motility did not differ significantly but post-freezing motility varied significantly (P<0.01) between seasons. Post-freezing motility was lowest during summer and highest during winter. It can be concluded that summer spermatozoa may be fragile and cannot withstand freezing stress. To increase reproductive efficiency in buffalo during summer, semen should be frozen during winter and spring and used during hot weather conditions. Seasonal variations in plasma LH levels were insignificant.