Specific interaction of vinculin with alpha-actinin

Vinculin and alpha-actinin are cytoskeletal proteins present at focal contacts of the ventral surface of cultured fibroblasts. We labelled alpha-actinin with an acceptor fluorophore and vinculin with a donor. A mixture of vinculin and alpha-actinin showed a 28% quench, due to energy transfer, suggesting an interaction. Quench of vinculin was dependent on the concentration of alpha-actinin; Scatchard analysis gives a dissociation constant in the microM range. Quench was inhibited by excess unlabelled alpha-actinin, and by reaction of the acceptor protein with p-chloromercuribenzoate. We found that vinculin had a slightly greater elution volume in a gel filtration column equilibrated with alpha-actinin, indicating a higher effective Stokes radius due to the interaction of the two proteins.     

Cloning and characterization of LOS1, a Saccharomyces cerevisiae gene that affects tRNA splicing.

Saccharomyces cerevisiae strains carrying los1-1 mutations are defective in tRNA processing; at 37 degrees C, such strains accumulate tRNA precursors which have mature 5' and 3' ends but contain intervening sequences. Strains bearing los1-1 and an intron-containing ochre-suppressing tRNA gene, SUP4(0), also fail to suppress the ochre mutations ade2-1(0) and can1-100(0) at 34 degrees C. To understand the role of the LOS1 product in tRNA splicing, we initiated a molecular study of the LOS1 gene. Two plasmids, YEpLOS1 and YCpLOS1, that complement the los1-1 phenotype were isolated from the YEp24 and YCp50 libraries, respectively. YEpLOS1 and YCpLOS1 had overlapping restriction maps, indicating that the DNA in the overlapping segment could complement los1-1 when present in multiple or single copy. Integration of plasmid DNA at the LOS1 locus confirmed that these clones contained authentic LOS1 sequences. Southern analyses showed that LOS1 is a single copy gene. The locations of the LOS1 gene within YEpLOS1 and YCpLOS1 were determined by deletion and gamma-delta mapping. Two genomic disruptions of the LOS1 gene were constructed, i.e., an insertion of a 1.2-kilobase fragment carrying the yeast URA3 gene, los1::URA3, and a 2.4-kilobase deletion from the LOS1 gene, los1-delta V. Disruption or deletion of most of the LOS1 gene was not lethal; cells carrying the disrupted los1 alleles were viable and had phenotypes similar to those of cells carrying the los1-1 allele. Thus, it appears that the los1 gene product expedites tRNA splicing at elevated temperatures but is not essential for this process.     

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.     

下丘脑外侧区注射TRH对大鼠胃酸分泌的影响

本文采用连续收集胃腔灌流法,观察下丘脑外侧区(LHA)注射促甲状腺激素释放激素(TRH)对大鼠胃酸分泌的影响,并分析TRH在LHA促进胃酸分泌的作用机制。结果表明:(1)LHA注射TRH(1μg)明显地刺激胃酸分泌;(2)预先向LHA注射酚妥拉明(10μg)、美多心安(5μg)及胃泌素抗体1μl(1:640)并不影响TRH的泌酸作用,如预先向LHA注射阿托品(5μg)则可消除TRH的泌酸效应;(3)垂体摘除及肾上腺切除均不影响TRH的泌酸作用;(4)隔下迷走神经切断后,LHA注入TRH的泌酸效应仍然出现,但持续时间显著缩短;腹腔交感神经节摘除后,TRH仍能促进胃酸分泌,但分泌量少而平稳。以上结果提示:LHA是TRH中枢泌酸效应的有关结构之一,其中枢机制是通过胆碱能M受体中介的,腹腔交感神经节和膈下迷走神经是TRH泌酸效应的传出途径。前者引起的泌酸反应出现较早且引起泌酸高峰,但持续时间短;后者则引起低平的持续分泌。     

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.