Plasmids are extrachromosomal genetic elements which in bacterial cells occur as entities physically separated from the chromosome and, as such, are capable of self-maintenance and self-replication for an infinitely long time. They are ubiquitous, being present in bacteria of nearly all systematic groups, and are also found in cells of a number of eukaryotes. When residing in bacteria, plasmids impart to them important properties, such as drug resistance, toxin production, and a capacity to degrade organic compounds. One of the most remarkable properties of many of them (conjugative plasmids) is the ability to transfer genetic information from the host (donor) bacteria to other (recipient) bacteria. This property is determined by the genetic region ha, which, as has been established for the F plasmid, comprises more than 20 genes and controls the synthesis of proteins that make possible both the conjugation of donor to recipient bacteria and DNA transfer from donors to recipients. Most of these genes have been traced to the operon traY--+ traZ [31,32,34,36,37].A positive regulator of the traY--, traZ operon in the F plasmid is the traJ gene, whose product is required for the transcription of this operon.The traJ gene, however, is itself under the negative control of the OP system's genes that prevent its expression and, consequently, the expression of the traY~ traZ operon [29,36]. Accordingly, as we noted earlier [17], the genetic regulation of F plasChair of Biology and General Genetics, Russian University of Peoples' Friendship, Moscow (Presented by D. S. Sarkisov, Member of the Russian Academy of Medical Sciences) mid transfer may be described as a "two-story" one, being positive at one "story" and negative at the other. Yet there also exists a traJ-independent transfer that is not acted upon by a product of the OP system. Rather, as shown in several studies, the traJ-independent transfer is acted upon by products of other genetic systems, including finQ, finU, finV, finW, and finC, identified in the genomes of self-repressed (rd) F-like and non-F-like plasmids [29,30,36].Thus, as can be seen from the above, the regulation of plasmid transfer is effected by many genes. However, we still do not know how many genes are actually involved in regulating plasmid transfer, what the number of such genes is and how they interact in the genomes of separate plasraids or in those of plasmids that form complexes in bacteria, and what are the origins of regulatory genes. All these questions led us to undertake studies aimed at identifying other genes regulating traJ-independent plasmid transfer, unraveling the mechanisms of their action and interaction, and tracing their origins.
SEEKING AND iDENTIFYING FIN SYSTEMS IN RD-TYPE PLASMIDSBefore a search for other possibly existing fin systems could be started, it was necessary to have, as indicators, plasmids of the derepressed (drd) type sensitive to inhibitors of plasmid transfers determined by already identified fin systems. For this reason, drawing upon the available knowl...
