Summary: R plasmids R40a, Rip69, R447b, R769 belonging to incompatibility groups A-C, M, N, V, respectively, were investigated for chromosomal mobilizing ability in . Plasmids R40a, Rip69 and R447b mediated polarized transfer of markers in a clockwise direction from origins near , and , respectively, on the linkage map. The recovery frequency per donor cell of proximal markers approached 1 × 10 for these three plasmids and the efficiency of chromosomal transfer was higher than that of the previously studied plasmid D. The plasmid-guided chromosomal trajectories overlap and it was possible to complement results obtained with plasmid D to assemble a time-of-entry chromosomal map and directly establish the circularity of the linkage group. The map comprises a length of 93 min in terms of transfer time. Plasmid R769 had a different pattern of chromosome transfer. This plasmid produced recombinants for all markers at frequencies of about 4× per donor. It effected multiple and more or less simultaneous entry of markers and produced recombination over lengths of chromosome rarely corresponding to more than 10 min on the linkage map.


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