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. Dispite of RNA-containing phages being among the best studied biosystems, some of their properties, especially phage-host inter­ actions, have not been completely investigated. One of the problems is a cause of multiple resistant cells development in E. coli cultures infected by RNA-containing phages in the conditions not favorable for quick cell division. In some previous papers concerning RNA-containing phages bio­ logy this phenomenon has been discussed from the point of view of pos­ sible preexisting mutants selection. Nevertheless, such an interpretation does not seem to be completely convincing because of large scale phage resistance development. In our previous paper [1] we have shown that more than 1 % of infected bacterium offspring receives MS2-resistance marker which may not be due to pre-existing mutants selection, We interpret such a fact as a non-direct proof of direct interactions bet­ ween phage genome and cell host DNA; out interpretation has been con­ firmed by non-stability of primary MS2-induced mutations and derivative forms segregation from these ones [2]. In order to prove that these mu­ tants properties are caused not by a persistent MS2 infection but due to phage genome integration into the host cell chromosome we have created a genetic library of EcoRI fragments of a segregant obtained by us — a lysing E. coli AB 259 Hfr 3000 mutant [3]. A total RNA preparation iso­ lated from plasmid-forming cells has been hybridised both with pMS27 DNA containing MS2 phage cDNA and with a part of this cDNA without vector sequence. The results obtained prove phage specific RNA to be transcripted from chromosomal DNA of the MS2-induced E. coli mutant; so we have really demonstrated that MS2 phage is able to establish true lysogeny as a state based on physical integration of phage and cellular DNA's. In the present paper we present our first data on our study of cloned host cell DNA fragment having the goal to determine how large is MS2-specific region and which is its localisation on the genetic map of our recombinant plasmid; we aim also to find there some recognition sites for several popular restrictive enzymes.

Lysogeny by MS2 phage. Analysis of a recombinant plasmid containing MS2 RNA-like sequence