[Z-form of intraphage DNA]

The bacteriophage lambda gt10 DNA containing an insertion of 20 pairs of GC-bases capable of being arranged as Z-form was cloned. Two independent methodological approaches based on the main properties of Z-form were used to study the shape of the insertion: formation of transition bridges composed of unpaired nucleotides between left-rotating Z-forms and right-rotating B-forms of helix (j-domain) and high immunogenic activity of Z-form. O-beta-diethylaminoethylhydroxyamine (OHA), an analogue of hydroxylamine, is capable of reacting specifically with unpaired cytidines. In this work this modification was used to inhibit the process of restriction at BamH1-site adjacent to (gc)10 insertion, that N-Methyl-bis(2-chloethyl) amine (MBCA) is capable of fixing the Z-form of the insertion in situ. Fixed Z-form is conserved even after DNA has been isolated from bacteriophage, thereby providing an opportunity of its identification by anti-Z-antibodies. It was shown that from 4 to 6% of the total number of insertions are in the Z-form. The hypothesis of significant role of Z-form in the process of packing of DNA molecules in capsid is put forward.