Evidence that the putative compatible solute 5-dimethylsulfoniopentanoate is an extraction artifact.

A novel gas chromatography-mass spectrometry method for analyzing sulfonium compounds as their S-demethylated silyl derivatives has clarified the origin of 5-dimethylsulfoniopentanoate. This compound, previously reported from flowers of Diplotaxis tenuifolia (L.) DC. (Cruciferae), is generated from glucoerucin during treatment with hot 6 N HCl. Glucoerucin is the characteristic glucosinolate of D. tenuifolia.     

Microscopic analysis of the effect ofRhizobium leguminosarum biovartrifolii host specific nodulation genes in the infection of white clovers

Summary A microscopic assessment is presented of the comparative infection capacity of wild-type and hybrid strains ofRhizobium leguminosarum bv.viciae withR. l. bv.trifolii strain ANU 843 on white clover seedlings. TheR. l. bv.viciae hybrid strains contained defined DNA segments coding for different combinations ofR. l. bv.trifolii host-specific nodulation genes. White clover plants were examined over a 72 h period to assessRhizobium infectivity, the morphological changes in root hair growth; colonisation ability of rhizobia; infection thread initiation and the ability to induce cortical cell division.R. l. bv.viciae strain 300 induced root hair curling more slowly than strain ANU 843 or any of the hybrid strain 300 bacteria, and when curling had taken place, there was poorer colonization by strain 300 within the folded hair cell, no evidence of infection thread formation and only limited cortical cell division 72 h after inoculation. The addition of the host-specific nodulation genes ofR. l. bv.trifolii to strain 300 was necessary to induce infection threads and establish a normal pattern of nodulation of the roots of white clovers.     

A DNA unwinding element and an ARS consensus comprise a replication origin within a yeast chromosome.

We have defined a replication origin, ORI305, within chromosome III of Saccharomyces cerevisiae by means of mutational analysis. cis-acting elements required for origin activity in the chromosome, as assayed by two-dimensional gel electrophoresis of replication intermediates, are the same as those required for the function of an autonomously replicating sequence, ARS305, in a plasmid. Essential elements include (i) an 11 bp sequence that is a near match to the ARS consensus and (ii) a broad sequence directly 3' to the consensus near match. Origin function is inactivated by point mutations in the essential near match sequence, suggesting that the sequence contributes to specifying the origin in the chromosome. Other consensus near matches with different sequences are present but are not required. The essential 3'-flanking sequence exhibits DNA helical instability and is sensitive to deletion mutations that stabilize the DNA helix. The wild-type 3'-flanking sequence can be functionally substituted by dissimilar sequences that also exhibit helical instability. The requirement for DNA helical instability indicates that the essential 3'-flanking sequence serves as a DNA unwinding element in the chromosome.     

Integration of simian virus 40 into cellular DNA occurs at or near topoisomerase II cleavage hot spots induced by VM-26 (teniposide).

Inhibition of DNA topoisomerase II in simian virus 40 (SV40)-infected BSC-1 cells with a topoisomerase II poison, VM-26 (teniposide), resulted in rapid conversion of a population of the SV40 DNA into a high-molecular-weight form. Characterization of this high-molecular-weight form of SV40 DNA suggests that it is linear, double stranded, and a recombinant with SV40 DNA sequences covalently joined to cellular DNA. The majority of the integrants contain fewer than two tandem copies of SV40 DNA. Neither DNA-damaging agents, such as mitomycin and UV, nor the topoisomerase I inhibitor camptothecin induced detectable integration in this system. In addition, the recombination junctions within the SV40 portion of the integrants correlate with VM-26-induced, topoisomerase II cleavage hot spots on SV40 DNA. These results suggest a direct and specific role for topoisomerase II and possibly the enzyme-inhibitor-DNA ternary cleavable complex in integration. The propensity of poisoned topoisomerase II to induce viral integration also suggests a role for topoisomerase II in a pathway of chromosomal DNA rearrangements.     

Mutagenesis analysis of a hepatitis delta virus genomic ribozyme.

We conducted extensive mutagenesis analysis on a hepatitis delta virus (HDV) genomic ribozyme to study the sequence specificity of certain region and to derive the secondary structure associated with the catalytic core. The results confirmed that the autocatalytic domain of HDV genomic RNA contained four base-pairing regions as predicted in the 'pseudo-knot' model [Perrotta & Been (1990) Nature 350, 434-436]. The size and sequence of one of the base-pairing regions, i. e. stem-and-loop, could be flexible. Helix 3 and the first basepair of helix 1 required specific sequence to retain self-cleavage activity. The structural requirement of helix 2 was less stringent than the other base-pairing regions. Moreover, the size of helix 1 affected self-cleavage whereas the length of hinge could be variable even though the first three residues of hinge had stringent sequence requirement.     

He—Ne激光对君子兰幼果和胡萝卜根的愈伤组织形成及生长的影响

利用6mv的He—Ne激光器,每天对君子兰幼果、胡萝卜根的外植体辐照5分钟,连续辐照20天,对愈伤组织的形成和生长有一定的促进作用。但同样条件下,辐照10分钟,对君子兰幼果,胡萝卜根的愈伤组织形成和生长都有明显的抑制作用。