DNA synthesis is initiated at two positions within the origin of replication of plasmid R1162.

DNA synthesis of broad host-range plasmid R1162 is initiated from two positions, flanking a large (40 bp stem, 40 bp loop) inverted repeat. Each start-point is located within a highly conserved, but oppositely oriented, 10 base-pair sequence. Synthesis from the two positions converges within the intervening inverted repeat. An analysis of deletions suggests that both start positions must be present for synthesis. A model describing possible early events in replication of plasmid R1162 is presented.     

Study of human chromosome V

Summary The induction of fragile sites on human chromosomes has been demonstrated under various conditions that cause thymidylate stress, including exposure to uridine. In this study, we examined common fragile site expression by initially exposing peripheral lymphocytes to uridine, followed by repair of the fragile sites with media containing various concentrations of thymidine. Lymphocytes were cultured in medium 199 with 2 mM uridine. At 0.5, 1, 2, 3, 8, 10, 12, and 18 h before harvest, the uridine medium was removed and replaced by medium containing thymidine at various concentrations. Our results demonstrate that the effect of uridine on chromosome fragility can be reversed by low concentrations of thymidine (2 M up to 200 M) and the rescuing effect of thymidine can be achieved if the cells were treated prior to 2–3 h before harvest. No repair was found if thymidine was added to culture within 2 h prior to harvesting, suggesting that packing of chromosomes is also an important factor in the expression and repair of fragile sites.     

Polygalacturonase activity and variation in ripening of papaya fruit with tissue depth and heat treatment

Effects of tissue position (viz. outer vs inner mesocarp) and heat treatment (48°C, 20 min) on variations in polygalacturonase (EC 3.2.1.15 and EC 3.2.1.67) activity and ripening of fruits of Carica papaya L. cv. Backcross Solo were investigated. Polygalacturonase activity increased during ripening concomitantly with an increase in tissue softness and soluble polyuronide level. Throughout ripening, inner mesocarp tissue was softer and contained higher polygalacturonase activity than outer mesocarp tissue. Titratable acidity as well as ß-galactosidase (EC 3.2.1.23) activity also increased during ripening; however, unlike polygalacturonase, their level or activity was lower in inner than in outer mesocarp. Ascorbic acid could partially account for the increase in titratable acidity during ripening but contributed very little to the differences in titratable acid levels between outer and inner mesocarp. Heat treatment had no effect on either fruit softness or titratable acidity, but it markedly reduced the increase in ascorbic acid and polygalacturonase activity during ripening. Ripening, as reflected by changes in tissue softness and polygalacturonase activity, progressed outwardly from the interior towards the exterior of the fruit. The effect of heat treatment in suppressing polygalacturonase activity was relatively greater in inner than in outer mesocarp, suggesting that sensitivity of the enzyme to heat treatment may vary with stage of ripeness of the tissue.     

Thermotolerance of isolated mitochondria associated with heat shock proteins

Mitochondria isolated from 2-day-old etiolated soybean (Glycine max) seedlings which had been subjected to various heat shock treatments, i.e. (A) 28°C (2 h), (B) 38°C (2 h), (C) 38°C (2 h)-42.5°C (0.5 h), and (D) 38°C (2 h)-42.5°C (0.5 h)-28°C (4 h), were monitored for O₂ uptake using an oxygen electrode. Mitochondria isolated after all four heat shock treatments were active in O₂ consumption at 28°C in response to succinate and ADP (derived P/O ratios were 1.6, 1.7, 1.3, and 1.3, respectively.) The mitochondria from all four treatments were also active in O₂ uptake at 42.5°C. However, only mitochondria isolated after treatment (C) were tightly coupling at 42.5°C (derived ADP/O ratio was about 1.4). Combined with our earlier findings on the subcellular localization of heat shock proteins, our present data demonstrate that association of heat shock proteins with mitochondria by treatment (C) enables them to phosphorylate at 42.5°C (i.e. they become thermotolerant). Isolated mitochondria from treatment (C) and treatment (A) were compared by electron microscopy. They appeared to be very similar and no significant ultrastructural differences were noted.     

Cloning and Expression of a Schwanniomyces occidentalis alpha-Amylase Gene in Saccharomyces cerevisiae

An alpha-amylase gene (AMY) was cloned from Schwanniomyces occidentalis CCRC 21164 into Saccharomyces cerevisiae AH22 by inserting Sau3AI-generated DNA fragments into the BamHI site of YEp16. The 5-kilobase insert was shown to direct the synthesis of alpha-amylase. After subclones containing various lengths of restricted fragments were screened, a 3.4-kilobase fragment of the donor strain DNA was found to be sufficient for alpha-amylase synthesis. The concentration of alpha-amylase in culture broth produced by the S. cerevisiae transformants was about 1.5 times higher than that of the gene donor strain. The secreted alpha-amylase was shown to be indistinguishable from that of Schwanniomyces occidentalis on the basis of molecular weight and enzyme properties.     

Influence of Co2+, Ni2+ and Fe2+ on the production of tetrapyrroles by Methanosarcina barkeri

Summary The selective formation of three tetrapyrroles, Co-containing corrinoids, Ni-containing factor F₄₃₀ and Fe-containing cytochromes (haems) by Methanosarcina barkeri Fusaro (DSM 804) was achieved as a function of the concentrations of Co²⁺, Ni²⁺ and Fe²⁺ in a methanol minimmum medium. It was found that about 70% of the total tetrapyrroles synthesized was excreted into the culture supernatant. Hence, the continuous production of tetrapyrroles in a fixed-bed reactor (supporter: porous diatomaceous clay) was carried out at a dilution rate of 10 day^-1 (850 ml medium/85 ml column/day). The effluent discharged from the reactor contained the excreted tetrapyrroles, the concentrations of which were dependent upon the Co²⁺, Ni²⁺ and Fe²⁺ concentrations in the feed medium. The maximum productivities from the reactor (1 l basis) were 52 M corrinoids/day, 24 M F₄₃₀/day and 8 M haems/day, respectively.     

大壁虎的染色体及减数分裂联会复合体的研究

大壁虎(Gekko gecko)的染色体数目为2n=38,核型由2对中着丝粒(Nos.1.4.)、3对亚中着丝粒(Nos.2.3.5)及14对端着丝粒和亚端着丝粒(Nos.6—19)染色体组成。一对核仁组织者(NOR_s),位于第7对端着丝粒染色体的末端。同时,本文还对大壁虎的减数分裂以及联会复合体(S.C)的结构和组型,进行了详细的观察和分析。     

Synthesis and duplex stability of oligonucleotides containing cytosine-thymine analogues.

The synthesis of the deoxynucleoside derived from the base P, 6H,8H-3,4-dihydro-pyrimido[4,5-c] [4,5-c] [1,2]oxazin-7-one, 2, and its introduction by established phosphoramidite and H-phosphonate chemistry into oligonucleotides is described. The melting transition temperatures (Tm) of a range of heptadecamer duplexes containing P/A and P/G base-pairs are compared with corresponding ones having N4-methoxycytosine (M) 1 and mismatched normal bases. P/A and P/G pairs allow closely similar duplex stabilities and have the potential to reduce the multiplicity of probes and primers based on amino acid sequences by removing the T/C degeneracy.