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.

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An octathymidylate derivative carrying an EDTA residue at its S-terminus was synthesized. In the presence of Fe'+, 02 and dithiotreitol, this derivative cleaves poly(dA) and poly(A) more efficiently than the non-complementary polynucleotide poly(dT). Affinity modification Nucleic acid Directed cleavage

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Phenylalanyl‐tRNA synthetase from Escherichia coli does not catalyze the [14C]phenylalanyl residue transfer from phenylalanyl‐adenylate to adenosine either in the presence or absence of homologous tRNAPhe and tRNAPhe −A. When the reaction mixture contained dithiothreitol, radioactive substance was detected having a mobility on HPLC column close to that of aminoacyladenosine. The amount of this product depended on the concentration of dithiothreitol in the mixture. Phenylalanyl residue was suggested to undergo transfer from aminoacyladenylate to dithiothreitol molecule.

Phenylalanine-specific tRNA from yeast was hydrolysed with cobra venom ribonuclease in the doublestranded regions and the fragments isolated. The 'dissected' molecules with nicks in positions 28 and 41were reconstructed from supplementary fragments and treated with T-4 RNA ligase. A phosphodiester bond between two fragments was formed when the fragment combination (l-28) + (29-76) was used. A strong discrimination in the ligation yield between different nick positions in the same helix is shown.Cobra venom nuclease RNA ligase

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