| Abstract: | The structures of two R-plasmids pWP14a and pWP12a (Tra-, Ap, Gm; 21 kb) and of several cointegrates they form with bacteriophages P1Cm and P1-15 were analyzed. In each case, replicon fusion was mediated by the element IS140 (about 0.8 kb), one copy of which resides on both plasmids adjacent to the gentamicin resistance determinant (AAC(3)-III). pWP14a cointegrated preferentially into or near the invertible C-loop structure of the P1 genome. Cointegrational mobilization of pWP14a was observed also with several conjugative R-factors. The process of replicon fusion is independent of the host's rec+ functions. Sequences homologous to IS140 are constituents of many R-factors, including RA1, R40a, R124, R144, Rts1, N3, and pJR255. IS140 also shows homology to two other sequences, IS15 delta and Tn2680, but not to other, well studied transposable elements. The ampicillin resistance determinant of pWP14a is within a Tn3-like transposon, Tn3651. |
