Mechanism of bleomycin: evidence for 4'-ketone formation in poly(dA-dU) associated exclusively with free base release

Incubation of poly(dA-[3'-3H]dU), poly(dA-[5'-3H]dU), or poly(dA-[5'-3H]dT) under a variety of conditions with activated bleomycin resulted in the production of free nucleic acid base, base propenal, and a small amount of 3H2O. Adjustment of the terminated reaction mixture to pH 10 and incubation at 95 degrees C resulted in a time-dependent increase in 3H2O to an amount equal to the amount of free base. If the terminated reaction mixture was incubated with NaBH4 prior to the heat and alkaline treatment, the release of 3H2O was significantly inhibited. These results are consistent with the generation by activated bleomycin of a 4'-ketone yielding free base, with the exchange of the 3'- and 5'-hydrogens by enolization and with the alkaline-induced strand scission occurring from this intermediate.     

A forced-air ventilation system for rodent cages

A novel forced-air ventilation system for rodent cages was developed. The apparatus was operated at an air flow rate of 56 L/min when used with a 230 mm wide X 450 mm long X 165 mm deep cage. Air velocity measurements in the cage did not exceed 8 m/min at animal (rat) height. The average NH3 concentration in a cage which housed two 250 g rats was less than 0.3 ppm at the end of the third day, whereas the concentration measured in a cage without the forced-air ventilation system was 150 ppm after 3 days. Tests of the water content of soiled bedding showed the forced-air ventilation system to provide a much drier environment for the rodents.     

Modification and processing of internalized signal sequences of prolipoprotein in Escherichia coli and in Bacillus subtilis

We have cloned the Escherichia coli lipoprotein structural gene (lpp) into a shuttle vector and studied its expression in both E. coli and in Bacillus subtilis. Using in vitro gene fusion techniques, the lpp gene was placed under the control of the promoter for the erythromycin-resistance (ery) gene. This fusion gene directed the synthesis of Braun's prolipoprotein which can be subsequently processed into the mature lipoprotein. In addition to the prolipoprotein, two ery-lpp hybrid proteins containing a 45- and a 22-amino acid extension preceding the NH2 terminus of prolipoprotein, respectively, are also synthesized in E. coli. The synthesis of these three proteins appears to involve the utilization of three distinct translation initiation sites. In B. subtilis, only two proteins are synthesized, the hybrid protein with a 45-amino acid extension and the prolipoprotein. In both E. coli and B. subtilis, the precursor forms of the hybrid proteins are lipid-modified, and they are processed to mature lipoprotein in vivo. These results indicate that internalized signal sequence containing the prolipoprotein modification and processing site (Leu-Ala-Glys-Cys) can function normally and permit the modification of hybrid proteins to lipid-modified precursors which can be subsequently processed by the globomycin-sensitive prolipoprotein signal peptidase.     

中国人ε珠蛋白基因5′侧序列中多态性Hinc Ⅱ位点的进一步研究

本文进一步研究了我国不同民族的正常个体以及β地中海贫血患者θ珠蛋白基因5′侧序列中的多态性HincⅡ位点及其遗传性质。在广西壮族正常个体和β地中海贫血纯合子中,该多态性位点的发生频率均为75％,与正常汉族人测得值相近。家系分析资料表明,该多态性位点完全按照孟德尔规律进行遗传。     

Computer control for continuous cultivation ofSaccharomyces cerevisiae

Summary An on-line respiratory quotient control system has been developed for the continuous cultivation of baker's yeast. This system is based on moving identification of the microbial dynamics. The optimal dilution rate that was selected as the control variable was determined by minimizing a performance index. Without resorting to complicated microbial analysis, a simple and practical moving model is obtained by continually updating the input and output data. The experimental results indicate the satisfactory controllability of the present system and the possible extention of the proposed method to other bioprocesses.     

Biosynthesis of Bacillus licheniformis penicillinase in Escherichia coli and in Bacillus subtilis.

Modified prepenicillinase was accumulated in both Escherichia coli and Bacillus subtilis treated with globomycin. Although the inhibitions of processings of prepenicillinase and prolipoprotein by globomycin in E. coli are qualitatively similar, they differ in the degree of inhibition at given concentrations of globomycin. The processing of prepenicillinase proceeds much more rapidly in E. coli than in B. subtilis.     

Models of Evolution of Reproductive Isolation

Mathematical models are presented for the evolution of postmating and premating reproductive isolation. In the case of postmating isolation it is assumed that hybrid sterility or inviability is caused by incompatibility of alleles at one or two loci, and evolution of reproductive isolation occurs by random fixation of different incompatibility alleles in different populations. Mutations are assumed to occur following either the stepwise mutation model or the infinite-allele model. Computer simulations by using It?'s stochastic differential equations have shown that in the model used the reproductive isolation mechanism evolves faster in small populations than in large populations when the mutation rate remains the same. In populations of a given size it evolves faster when the number of loci involved is large than when this is small. In general, however, evolution of isolation mechanisms is a very slow process, and it would take thousands to millions of generations if the mutation rate is of the order of 10(-5) per generation. Since gene substitution occurs as a stochastic process, the time required for the establishment of reproductive isolation has a large variance. Although the average time of evolution of isolation mechanisms is very long, substitution of incompatibility genes in a population occurs rather quickly once it starts. The intrapopulational fertility or viability is always very high. In the model of premating isolation it is assumed that mating preference or compatibility is determined by male- and female-limited characters, each of which is controlled by a single locus with multiple alleles, and mating occurs only when the male and female characters are compatible with each other. Computer simulations have shown that the dynamics of evolution of premating isolation mechanism is very similar to that of postmating isolation mechanism, and the mean and variance of the time required for establishment of premating isolation are very large. Theoretical predictions obtained from the present study about the speed of evolution of reproductive isolation are consistent with empirical data available from vertebrate organisms.     

Evidence for cAMP-independent inhibition of S-phase DNA synthesis by prostaglandins

Two prostaglandins, prostaglandin E1 (PGE1) and prostaglandin B1 (PGB1), block S-phase DNA synthesis in synchronous cultured baby hamster kidney (BHK) cells. The prostaglandin inhibition of DNA synthesis does not appear to require elevated levels of cAMP. In BHK-21 cells that have been "desensitized" to prostaglandin stimulation of adenylate cyclase and, therefore, have control levels of cAMP, PGE1 retains its inhibitory effect on the incorporation of tritiated thymidine into DNA. When BHK cells are exposed to PGB1 (a prostaglandin that does not elicit a cAMP response), DNA synthesis is also blocked. In nonsynchronous cells exposed for 1 h to PGE and then incubated for 1 h with PGE removed, a rebound of DNA synthesis occurs, therefore providing evidence that a transient rise of cAMP in itself is not capable of causing a cascade of reactions that block the synthesis of DNA. In addition, the concentration of PGE required for inhibition of DNA synthesis is significantly less than that required for cAMP generation. Addition of 1 x 10(-8) M PGE to BHK cells can be shown to significantly inhibit DNA synthesis within 30 min, with half-maximal inhibition seen at 3 x 10(-7) M PGE. Cyclic AMP levels for controls were 4.9 +/- 0.2 and 4.6 +/- 0.1 for 1 x 10(-6) M PGE1. These findings suggest that the prostaglandins can act independently of cAMP at physiological concentrations; and, therefore, it is possible that prostaglandins have a physiological role in the control of cell growth during S-phase.