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.

Oligo(U) derivatives with [14C]-4-(N-2-chloroethyl-N-methylamino)benzaldehyde attached to 3'-end cis-diol group via acetal bond, p(Up)n-1UCHRCl as well as with [14C]-4-(N-2-chloroethyl-N-methylamino)benzylamine attached to 5'-phosphate via amide bond, ClRCH2NHpU(pU)6 were used to modify 70S E. coli ribosomes near mRNA binding centre. Within ternary complex with ribosome and tRNAPhe all reagents covalently bind to ribosome the extent of modification being 0.1-0.4 mole/mole 70S. p(Up)n-1UCHRCl alkylates either 30S (n=5,7) or both subunits (n=6,8). rRNA is preferentially modified within 30S subunit. ClRCH2NHpU(pU)6 alkylates both subunits the proteins being mainly modified. The distribution of the label among proteins differ for various reagents. S4, S5, S7, S9, S11, S13, S15, S18 and S21 are found to be alkylated within 30S subunit, proteins L1, L2, L6, L7/L12, L19, L31 and L32 are modified in the 50S subunit. Most proteins modified within 30S subunit are located at the "head" of this subunit and proteins modified within 50S subunit are located at the surface of the contact between this subunit and the "head" of 30S subunit at the model of Stoffler.

Heptauridylate bearing a radioactive alkylating [14C]-4-(N-2-chloroethyl-N-methylamino)benzylamine attached to the 5'-phosphate via amide bond, was bound to ribosomes and small ribosomal subunits from rat liver which thereby were coded to bind N-acylated Phe tRNA. After completion of the alkylating reaction and subsequent hydrolysis of the phosphamide bond ribosomal proteins were isolated. Radioactivity was found covalently associated preferentially with protein S26 and, to a very small extent, with proteins S3 and S3a. The affinity labelling reaction could be abolished by (pU)14 and poly(U). From the results it is concluded that ribosomal protein S26 is located at the mRNA binding site of rat liver ribosomes.

Chemical modification of the chromatin DNA with alkylating derivatives of oligothymidylate (pT)16 and oligoadenylate (pA)16 bearing 4-(N-2-chloroethyl-N-methylamino)benzylphosphamide group at the 5'-phosphate has been investigated. It was found that the derivatives do react with DNA in chromatin. The reactions occur presumably at the complementary sequences of the DNA since the reaction of the oligothymidylate derivative is inhibited by oligonucleotide (pT)16 taken in excess and is not influenced by hexadecanucleotide of a random structure. Isolated DNA does not react with the oligothymidylate derivative. It is concluded that in chromatin, DNA is partially unwound or possesses some sites which can be opened easily in the presence of complementary oligonucleotides.

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.