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.     

Nuclear magnetic resonance study on the exchange behavior of the NH-N protons of a ribonucleic acid miniduplex

The exchange behavior of the guanine N(1) and uracil N(3) protons in the self-complementary hexanucleotide r(ApApGpCpUpU) has been studied at 5 degrees C in 80% H2O/20% D2O by proton NMR. Under these conditions, the hexanucleotide forms a stable miniduplex. The exchange rate of all Watson-Crick NH protons is unaffected by addition of trifluoroethylamine up to 0.07 M. On the other hand, addition of phosphate buffer, pH 6.9, enhances the exchange rate of the uracil N(3) protons of both terminal and internal A X U base pairs but does not influence the exchange rate of the guanine N(1) protons of the central G X C base pairs. Catalysis by increased phosphate concentrations results in an open-limited rate of the internal A X U base pairs with kex = 233 s-1, equivalent to a lifetime of 4.3 ms. The proton exchange of the central G X C is regulated by the opening rate of the central core of the miniduplex. On the other hand, the sensitivity of the exchange rate of internal as well as of terminal A X U base pairs can be explained by their reduced lifetime due to end "fraying" and a subsequent catalysis of the exchange process from the opened state. These results suggest that it may be possible to probe labilized parts of RNAs such as tRNA by gradual addition of the exchange catalyst phosphate and to monitor their exchange rates by proton NMR.     

Periodic conformations of deoxyribonucleic acids

The conformation of a deoxyribonucleotide unit in a deoxyribonucleic acid molecule can be defined by six angles, each of which specifies the relative orientations between two groups of atoms adjacent to a covalent bond. With the assumption that these atoms are hard spheres with fixed van der Waal radii, conformations are sought to minimize their overlapping. The additional requirement of the polymer having a periodic structure further reduces the allowable conformations.     

高胆固醇高脂肪膳食对家兔β-VLDL组成及其与巨噬细胞相互作用的影响的初步研究

给家兔喂以1％胆固醇及10％菜油(A组)或猪油(B组)50多天后A组血胆固醇水平(824.2±265.1mg/dl)明显低于B组(1666±693.8mg/dl);A组甘油三酯水平(51.9±19.1mg/dl)亦低于B组(104±40.2mg/dl)。二组家兔的β—VLDL的脂类组成无差别,但A组β—VLDL的apoE高于B组,分别为45.2％及37.5％。高分子量apoB(apoB_h)为33.6％,低于B组β-VLDL(47.3％)。A组β-VLDL促进小鼠腹腔巨噬细胞胆固醇堆积的程度大于B组,可能与apoE含量高有关。我们认为多不饱和脂酸减轻动脉粥样硬化(As)的作用不在于改变脂蛋白构成后阻碍泡沫细胞的形成而是促进β—VLDL从体内清除。     

Protein synthesis and secretion in the human epididymis and immunoreactivity with sperm antibodies

The synthesis and secretion of proteins in the different regions of the human epididymis were studied in vitro. Epididymal tissues obtained from patients undergoing castration for prostatic carcinoma or from cadavers were incubated in the presence of [35S]methionine, and the resulting radiolabeled proteins were analysed on SDS-PAGE. The corpus region was found to be the most active segment in total protein synthesis. Significant qualitative and quantitative changes were observed in the pattern of proteins secreted from the different epididymal regions. To establish those epididymal proteins that interact with maturing sperm, the secreted products were immunoreacted with antibodies raised against a Triton X-100 extract of ejaculated human sperm heads. The antibodies react mainly with the head region of ejaculated spermatozoa as judged by indirect immunofluorescence. Protein A-gold labeling of freeze-fracture images showed gold particle distribution on the sperm plasma membrane. Western blot analysis of the secreted proteins revealed four bands (66, 37, 32, and 29 kDa) in the proximal regions and six additional bands (80, 76, 48, 27, 22, and 17 kDa) in the distal part of the epididymis. Immunoprecipitation of the secreted proteins with these antibodies revealed six radioactive bands of 170, 80, 76, 60, 48, and 37 kDa, which indicates that certain proteins of epididymal origin bind to the sperm plasma membrane.     

Adherence Patterns and DNA Probe Types of Escherichia coli Isolated from Diarrheal Patients in China

One hundred and seventy-two strains of Escherichia coli isolated from diarrheal patients in Beijing, P. R. China, were analyzed for plasmid DNA profile, HEp-2 cell adherence ability and reactivity to 10 previously described DNA probes. They had not been recognized as pathogenic E. coli in China. Of the 110 strains tested, 76 (69%) contained one or multiple large plasmids. Of the 71 strains with the large plasmids 64 could adhere to HEp-2 cells. Of the 172 strains, 102 (59.3%) were hybridized with at least one of the 10 probes. Of those, seven strains hybridized with enteroaggregative E. coli (EAggEC) probe. Their serotypes were O128 (two strains), O6 (one strain), and O111 (one strain). Three strains were untypable. Six and three strains were hybridized with enteropathogenic E. coli (EPEC) attaching and effacing genes (eae) or EPEC adherence factor (EAF) probe, respectively. Two non-O157: H7 strains hybridized with enterohemorrhagic E. coli (EHEC) probe. Seventy-two strains (41.9%) hybridized with shiga-like toxin 2 or 1 (SLT2 or SLT1) probes. Among the SLT1 or SLT2 probe-positive strains, 54 hybridized with invasive (INV) plasmid probe developed for identification of enteroinvasive E. coli (EIEC) and Shigella species. The INV and SLT probe-positive strains might represent a new variety of verotoxin-producing E. coli (VTEC).     

中国貂祝蛾属研究及二新种记述(鳞翅目：祝蛾科)

中国貂祝蛾属研究及二新种记述（鳞翅目：祝蛾科）武春生（中国科学院动物研究所北京１０００８０）貂祝蛾属ＡｔｈｙｍｏｒｉｓＭｅｙｒｉｃｋ,１９３５曾一直是瘤祝蛾亚科（Ｔｏｒｏｄｏｒｉｎａｅ）中的一个单型属,分布于我国和日本。其前翅的Ｍ２＋３合并,且靠近共...