Transcriptional activity of <i>repABC</i> operons of <i>Rhizobium leguminosarum</i> bv. <i>trifolii</i> TA1 plasmids: (A) pRleTA1a, (B) pRleTA1b, (C) pRleTA1c, and (D) pRleTA1d.

<p>Left panels show schematic genetic organization of the <i>repABC</i> cassettes. White arrows represent <i>repA</i>, <i>repB</i> and <i>repC</i> genes, and white broken arrows depict <i>repA</i> genes. Black dots show the position of <i>parS</i>-sites. The identified promoters of <i>repABC</i> operons were marked as grey rectangular boxes. The respective DNA fragments necessary for particular promoter identification, operon structure assignment, as well as their sequential deletions used for operon regulation studies, which were cloned into pMPK reporter and pBBR1MCS-5 vectors, were shown as black lines with positions indicated relative to <i>repA</i> start codon. The following system was applied for pMPK- and pBBR-1MCS5-based constructs nomenclature: e.g. in pMa/A2 recombinant plasmid the first two letters (pM) mean the shortcut of vector name (pMPK in this case), the next small letter 'a' means that it is derivative of pRleTA1a <i>repABC</i> cassette, the capital letter A followed by slash means that the cloned fragment comprise entire <i>repA</i> gene (in the case of pMa-d/ABC2 constructs the cloned fragments encompass entire <i>repA</i> and <i>repB</i> genes and fragment of <i>repC</i> fused with <i>lacZ</i>). Respectively, pBa/A2 means the same fragment recloned to the pBBR-1MCS5. Right panels represent β-galactosidase activities of respective <i>lacZ</i> transcriptional fusions measured in <i>A</i>. <i>tumefaciens</i> and expressed in Miller units. Each value (with standard deviation—extended bars) is the average of at least three independent measurements.