Alternative approach to the numerical synthesis of the dense-ion-beam focusing systems.

An alternative approach has been developed to the numerical synthesis of ion-beam focusing systems that prepare the dense laminar ion beams with the required profile of the ion trajectories. Conventionally an ill-posed synthesis problem arises in such cases, and only low-density beams with no magnetic field are treated. Instead, we compute both the electric and magnetic fields by considering two well-posed problems, the first for the equivalent potential Q and the second for the electric potential U. An analytical solution for Q for the specific case of an axial system has been found and a self-consistent method of satisfying the axial boundary conditions for Poisson's equation in U is described. It is shown that the beam can be focused while preserving its laminar structure and the required profile when applying various superpositions of both the electric and magnetic fields.

Endogenous oligonucleotides of human milk and their possible biological function.

Oligonucleotides (ON) 4 to 60 nucleotides in length were isolated by ion-exchange chromatography on a column with Fractogel TSK DEAE-650 (M) from human milk which was hydrolyzed with proteinase K. ON from 60 to 16 nucleotides were degraded by RNase A but were resistant to DNase I, and, thus, they were ribooligonucleotides. In the presence of [gamma-32P]ATP, ON and heparin inhibited the phosphorylation of 38- and 20-kD milk proteins and failed to affect the phosphorylation of a 76-kD protein. Human milk is believed to contain polyanion-dependent and polyanion-independent protein kinases. The influence of the ON on the activity of the cytotoxic fraction of human milk alpha-lactalbumin towards human mammary gland carcinoma MCF-7 cells was studied. The ON inhibited the cytostatic and cytotoxic effects of alpha-lactalbumin. Synthetic oligonucleotides and heparin had similar effects. The endogenous ON are suggested to be involved in the regulation of cytotoxic activity of human milk.

Mechanism of oligonucleotide uptake by cells: involvement of specific receptors?

We have investigated the interaction of oligonucleotides and their alkylating derivatives with mammalian cells. In experiments with L929 mouse fibroblast and Krebs 2 ascites carcinoma cells, it was found that cellular uptake of oligodeoxynucleotide derivatives is achieved by an endocytosis mechanism. Uptake is considerably more efficient at low oligomer concentration (less than 1 microM), because at this concentration a significant percentage of the total oligomer pool is absorbed on the cell surface and internalized by a more efficient absorptive endocytosis process. Two modified proteins were detected in mouse fibroblasts that were treated with the alkylating oligonucleotide derivatives. The binding of the oligomers to the proteins is inhibited by other oligodeoxynucleotides, single- and double-stranded DNA, and RNA. The polyanions heparin and chondroitin sulfates A and B do not inhibit binding. These observations suggest the involvement of specific receptor proteins in binding of oligomers to mammalian cells.

Synthesis of alkylating oligonucleotide derivatives containing cholesterol or phenazinium residues at their 3'-terminus and their interaction with DNA within mammalian cells.

5'-[32P]-labelled alkylating decathymidylate [4-(N-2-chloroethyl)N-methylaminobenzyl]-5'-phosphamide derivatives containing cholesterol or phenazinium residues at their 3'-termini were synthesized and used for alkylation of DNA within mammalian cells. The uptake of the cholesterol derivative by the cells and the extent of DNA alkylation are about two orders of magnitude higher than those of a similar alkylating derivative lacking the groups at the 3'-termini. The presence of the phenazinium residue at the 3'-terminus of the oligonucleotide reagent does not improve the reagent uptake by the cells but drastically increases the DNA modification efficiency.

Nucleotide and oligonucleotide derivatives as enzyme and nucleic acid targeted irreversible inhibitors. Biochemical aspects.

Sequence specific modification of nucleic acids with reactive oligonucleotide derivatives, complementary addressed modification, can provide an efficient approach for specific inactivation of certain cellular nucleic acids. In experiments with ascites tumor Krebs II cells and alkylating oligothymidylate derivatives it was found that alkylating oligonucleotide derivatives enter the living cell and modify complementary sequences in cellular nucleic acids with high efficiency. Complementary addressed modification of poly(A) sequences in cellular RNA with oligothymidylate derivatives was investigated in detail. The results of experiments on alkylation of cellular nucleic acids are consistent with complementary addressed modification of poly(A) sequences in cellular DNA. These results are supported by experiments on modification of chromatin DNA in which it was found that chromatin DNA interacts with oliogothymidylate derivatives more readily than the isolated double stranded DNA. It was found that alkylating oligonucleotide derivatives complementary to a sequence in immunoglobulin mRNA of MOPC 21 cells arrest the cellular immunoglobulin synthesis. Alkylating oligonucleotide derivatives complementary to RNAs of fowl plague virus inhibit virus multiplication in cell culture.