Affinity modification of human chromatin with reactive derivatives of oligonucleotides

Reaction of 4-(N-2-chloroethyl-N-methylamino)benzylphosphamides of oligonucleotides (RCl-(pT)16 and RCl-(pApC)6) with human chromatin in intact nuclei and with metaphase chromosomes has been investigated. The oligonucleotides were targeted to poly(A) and poly(TG)-repeating DNA sequences. It was found that the reagents alkylate DNA and some proteins due to specific complex formation. The affinity character of the reaction was proved by the fact that free corresponding oligonucleotides taken in excess or preliminary treatment of chromatin with S1-nuclease both prevent the biopolymers from modification. The results obtained evidence that in human chromatin there are open DNA sequences available for affinity modification with oligonucleotide derivatives. Analysis of patterns of modified proteins within these chromatin areas may give a key to the structure of these chromatin sites.