Periodic cleavage of poly(dA) by oligothymidylates covalently linked to the 1,10-phenanthroline-copper complex

1,10-Phenanthroline (OP) was covalently attached to the 3'-terminus of two oligothymidylates via different linkers [abbreviated as T8-(OP) and T6-(OP)]. In the presence of Cu2+ and 3-mercaptopropionic acid (MPA), these reagents induce a hybridization-dependent cleavage of poly(dA) and of a 27 nucleotide long oligodeoxynucleotide containing an A8 sequence. The principal cleavage sites on the 27-mer span four residues located near the 3'-terminal phosphate group of T8-(OP). When poly(dA) was degraded by T6-(OP) and T8-(OP), a series of bands were obtained corresponding to a repeat unit of six and eight nucleotides, respectively. This periodicity reflects the cooperative binding of oligothymidylate-OP to the polynucleotide matrix and the localized nicking sites.     

Alternate pathways of DNA replication in Escherichia coli

We have described the pcbA1 mutation which enables E. coli cells to replicate DNA in the absence of a functional dnaE gene product if DNA polymerase I (the polA gene product) is present. The pcbA1 mutation phenotypically suppresses multiple dnaEts and dnaEam alleles. The pcbA1/PolI replication pathway differs from normal in sensitivity to certain DNA-damaging agents such as methylmethane sulfonate (MMS) and a lack of damage-directed mutagenesis. We report here cloning of the pcbA1 gene in a multicopy plasmid. The pcbA1 mutation is detected only in cis; therefore, cloning necessitated gene eviction. The pcbA1 gene lies closely- linked to gyrB. We have demonstrated the physical presence of DNA polymerase I in the replicating holoenzyme complex by immunoblotting using dnaEam strains. We conclude that E. coli has two alternate replisome structures: REP-A, in which DNA polymerase I is the functional synthetic subunit; and REP-E, in which the alpha-subunit, product of the dnaE gene, is functional. To investigate further the role of individual DNA polymerases in replication, we have isolated the polB gene on multicopy plasmids.     

Repair of potentially lethal radiation damage in confluent and non-confluent cultures of human hybrid cells

The repair of potentially lethal damage (PLDR) in a gamma-irradiated human hybrid cell line (skin fibroblast X HeLa) and its tumourigenic segregant has been studied as a function of cell density at the time of irradiation and during the postirradiation repair period. The data show that PLDR occurs in both non-confluent and confluent cultures of both cell lines. Furthermore, there is evidence that the extent of PLDR is dependent on cell density and that cell-cell contact may be an important factor in this regard.     

长叶车前花叶病毒(HRV_(sh))外壳蛋白赖氨酸残基的修饰

我们曾报道长叶车前花叶病毒上海分离株(简称HRVsh)的外壳蛋白有二个赖氨酸残基,在PH8.5无变性剂存在的条件下,完整病毒颗粒表面的赖氨酸残基可与三硝基苯磺酸(TNPS)起反应,反应后的TNP-HRVsh病毒颗粒的感染力丧失达90％以上。 本文又进行了甲基乙亚胺甲酯(MEI)对HRVsh赖氨酸残基的修饰反应,修饰后的MEI-HRVsh病毒颗粒的感染力也同样丧失90％以上。 从三硝基苯磺酸修饰的病毒颗粒(TNP-HRVsh)中分离得到的RNA能与天然的HRVsh的外壳蛋白重建病毒颗粒,并具有感染力,说明修饰过程中核酸并不受影响。 进一步用同位素~(35)S,~(32)P双标记病毒,再以TNPS修饰标记的病毒,得到(~(35)S,~(32)P)-HRVsh及TNP-(~(35)S,~(32)P)-HRVsh。将两者分别接种于系统寄主青菜(Brassica chinensis)的一片叶片,一天后在非接种叶片上都可测得~(35)S,~(32)P的放射计数。其中,(~(35)S,~(32)P)-HRVsh的~(35)S/~(32)P比值降低了,而TNP-(~(35)S,~(32)P)-HRVsh的~(35)S/~(32)P比值保持不变。说明HRVsh外壳蛋白赖氨酸残基的修饰并不影响病毒颗粒进入寄主细胞,以及在寄主细胞间的转移。同位素双标记的结果表明,其感染力丧失的原因可能是由于上述修饰作用阻止了病毒在感染中所必须的脱壳过程。     

我国东喜马拉雅及其邻区牛肝菌目的研究（续）

本属与多种树种有菌根关系：如Pinus,Larix,Abies和Pseudotsuga,但在Larix林下,本菌往往与土壤中的鞣料相聚集,对周围某些植物根系不利。本属现知15种,本区6种。     

Murine polyspecific antibodies. I. Monoclonal and serum anti-DNA antibodies cross-reactive with 2,4,6-trinitrophenyl derivatives

Six anti-DNA hybridoma autoantibodies were prepared by fusing spleen cells from unimmunized MRL/MpJ/lpr/lpr female mice with BALB/c myeloma cells. The monoclonal antibodies were analyzed by solid-phase ELISA for antigen-binding specificities. Three antibodies (62A2, 85A5, and 43B2) bound ssDNA, TNP-KLH, and recognized an epitope(s) present on insolubilized proteins such as BSA, KLH, ferritin, and insulin. The antibodies bound, with a marked preference, TNP-KLH, either soluble or insoluble. The other three antibodies (35A1, 32C5, and 39D2) bound only ssDNA. However, this binding was inhibited by free flavinic acid. None of the six antibodies bound either cardiolipin or proteoglycans, indicating that they do not recognize the repeating negatively charge units common to cardiolipin, proteoglycans, and DNA. All six monoclonal antibodies were purified by affinity chromatography with TNP-Sepharose. Moreover, both anti-DNA and anti-TNP antibodies from sera of nonautoimmune and autoimmune mice were purified easily on TNP-Sepharose.     

Cell-cell interaction can influence drug-induced differentiation of murine embryonal carcinoma cells

When cultured in the presence of either retinoic acid (RA) or dimethyl sulfoxide (DMSO), aggregates of the P19 line of mouse embryonal carcinoma (EC) cells differentiate and the spectrum of cell types formed depends on the drug dose. It is shown here the EC cells rapidly lose their colony-forming ability when cultured as aggregates in the presence of DMSO. This loss of plating efficiency (PE) also occurs rapidly following RA treatment. Loss of PE has been used as a quantitative procedure for assessing the rate of drug-induced differentiation. The relationship between drug dose and loss of PE is much steeper for DMSO than for RA, suggesting that these two drugs affect different stages of the differentiation decision-making apparatus. Mutant EC cell lines (D3 and RAC65) do not differentiate in the presence of drug-inducers (DMSO and RA, respectively). Neither differentiation-deficient mutant has an altered ability to form gap junctions. When D3 and P19 cells were mixed within the same DMSO-treated aggregates, the D3 cells remained undifferentiated and the P19 cells differentiated much less efficiently than if they were cultured in the absence of the D3 cells. When RAC65 and P19 cells were mixed in RA-treated aggregates, each cell responded to the drug as though the other were absent. Thus RA behaves as a cell-autonomous inducer of differentiation, whereas DMSO-induced differentiation seems to be mediated by interactions between neighboring cells.     

Three types of transmitter release from embryonic neurons

Prior to the contact with their target muscle cells in culture, growth cones of many isolated Xenopus embryonic neurons release acetylcholine (ACh) spontaneously. Using patch clamp techniques, this release can be detected by an outside-out patch of muscle membrane placed near the growth cone. Intracellular recording from innervated muscle cells showed spontaneous miniature endplate potentials (MEPPs) of varying amplitudes. Amplitude histograms showed a skewed distribution with multiple peaks, suggesting the existence of subunits in either the quantal packages of ACh released by the nerve terminal or in the postsynaptic muscle response. In addition to the quantal ACh release reflected by MEPPs, nerve terminal also release a large amount of ACh in a non-quantal fashion. This non-quantal ACh release is revealed by the hyperpolarization of the muscle membrane following extracellular application of curare or alpha-bungarotoxin, as well as by denervation of the muscle cell.