Ligands of second generation platinum analogs decrease both platinum-induced DNA cross-linking and its ability to interact with 1-beta-D-arabinofuranosyl cytosine to potentiate cytotoxic efficacy

We evaluated the cytotoxic and DNA cross-linking (CL) ability of four second generation platinum coordination complexes (TNO-6, JM-89, JM-8 and JM-9) delivered alone or in combination with 1-beta-D-arabinofuranosyl cytosine (ara-C) to human colon cancer cells (LoVo). Cell survival varied markedly as a function of the particular substitution moiety. JM-8 and JM-9 were virtually ineffective, even at concentrations as high as 50 micrograms/ml. At that concentration cis-diamminedichloroplatinum(II) (cis-DDP) killed greater than 99.99% of the cells. JM-82 was slightly more active while TNO-6 was the only derivative with appreciably higher cytotoxic activity due to an abrogation of the shoulder region of the type C survival curve. The highest CL effect was observed for cis-DDP followed closely by TNO-6. Very little CL effects were demonstrated for the other three analogs JM-82, JM-8 and JM-9 when measured 6 h after treatment. The combination of cis-DDP and ara-C augmented 10-fold the cytotoxic activity of cis-DDP alone, an effect accompanied by an almost 2-fold increase in CL; every other analog failed to interact in a potentiating manner (either cytotoxicity, or CL at 6 h) with the antimetabolite. Thus, it appears clear that the associated moieties of the Pt coordination complex play a fundamental role in reducing the interaction of the analogs with DNA (as reflected by the decreased CL and cytotoxic effects produced by each agent alone) and in totally preventing their interaction with ara-C to yield a potentiating lethal effect.     

Molecular Mechanisms of Translation Initiation in Mammals Studied by in vitroReconstruction of Initiation Complexes

Papers on the mechanisms of translation initiation in mammals studied by reconstruction of initiation complexes from individual components are reviewed. The author points to the constraints of this approach and to the pitfalls ignoring which one might come to erroneous conclusions and even artifacts. In addition, some methods employed in the field as well as some technical problems are discussed in the paper, together with the means of obviating them. The review could be a guidebook for newcomers into this quite labor-consuming field.     

Cloning of aroG, the gene coding for phospho-2-keto-3-deoxy-heptonate aldolase(phe), in Escherichia coli K-12, and subcloning of the aroG promoter and operator in a promoter-detecting plasmid

Defective transducing phages carrying aroG, the structural gene for phenylalanine (phe)-inhibitable phospho-2-keto-heptonate aldolase (EC 4.1.2.15; previously known as 3-deoxy-D-arabinoheptulosonate-7-phosphate synthetase[phe]), have been isolated, and DNA from two of these phages has been used to construct a restriction map of the region from att lambda to aroG. A 7.6-kb PstI-HindIII fragment from one of these phages was cloned into pBR322 and shown to contain aroG. The location of aroG within the 7.6 kb was established by subcloning and Tn3 transpositional mutagenesis. A fragment carrying the aroG promoter and operator has been cloned into a high copy number promoter-cloning vector (pMC489), and the resulting aroGpo-LacZ' (alpha) fusion subcloned in a low copy number vector. Strains with this fusion on the low copy number vector exhibit negative regulation of beta-galactosidase expression by both phenylalanine and tryptophan and positive regulation by tyrosine in a tyrR+ background.     

Action of pilocarpine on the normal frog heart and in pathology

Experiments on frogs were performed to examine the effect of the M-cholinomimetic pilocarpine on the heart. It was discovered that at concentrations of 10(-15)--10(-5) g/ml pilocarpine exerted only an adverse chronotropic effect on the perfused heart. When applied at a concentration of 10(-4) g/ml the drug produced a negative as well as a positive chronotropic effect. The latter occurred spasmodically (without progressive rise in the heart rate) in association with a slow heart rate. In some experiments such effects were preceded by a certain deceleration of the heart. In experiments with positive chronotropic effects, arrhythmias and sinoatrial dissociation were observed sometimes. Experiments with recording of the electrograms of the sinuses and lower parts showed that such effects were caused not by pacemaker acceleration but by the removal of the blockade of conduction, between the pacemaker and the atria. As far as the pacemaker is concerned, pilocarpine exerted only a negative chronotropic effect.     

A rapid single-stranded cloning strategy for producing a sequential series of overlapping clones for use in DNA sequencing: application to sequencing the corn mitochondrial 18 S rDNA

A simple new procedure was described for producing a sequential series of overlapping clones for use in DNA sequencing. The technique used single-stranded M13 DNA and complementary DNA oligomers to form specific cleavage and ligation substrates. It was, therefore, independent of the sequence of the DNA cloned into the vector. Deletions of varying sizes were generated from one end of the insert through the 3' to 5' exonuclease activity of T4 DNA polymerase. The approximate size of the deletion and therefore the starting point for DNA sequencing could be estimated by electrophoresis of the subcloned phage DNA on a agarose gel. This greatly reduced the number of templates that must be sequenced to obtain a complete sequence. The entire procedure could be carried out in one tube in less than a day. The procedure was used to subclone and sequence the maize mitochondrial 18 S rDNA and 5' flanking region (2622 bases) in less than a week. Other applications of oligomers and single-stranded DNA in the construction of insertions, deletions, and cDNAs are discussed.