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A 3.6‐kbp segment from the vir region of Ti plasmids contains genes responsible for border sequence‐directed production of T region circles in E. coli
Author(s) -
AltMoerbe Juliane,
Rak Bodo,
Schröder Joachim
Publication year - 1986
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1986.tb04337.x
Subject(s) - physics , biology , plasmid , gene , humanities , genetics , philosophy
The vir region of Ti plasmids is responsible for the transfer of the T region from Agrobacteria to plant cells; previous experiments suggested that formation of independent T region DNA circles is one step in this process. To study this step in Escherichia coli , we developed a binary vector system. One plasmid (=substrate) contains correctly oriented right and left borders from octopine plasmid pTiAch5. A gene with a counterselectable function ( gal K) was cloned between these borders. The gal K gene is under the control of the tac promoter–operator and the lac repressor with the lac i gene also in the selection cassette. This construction allows determination of substrate plasmid mutants which have lost the selectable gal K function. The second component of the system is one of a set of compatible plasmids harbouring various cloned parts from the vir region of nopaline plasmid pTiC58. A 3.6‐kbp segment of the vir region turned out to be necessary and sufficient for production of substrate plasmid mutants which represented the equivalent of the T region containing a complete left border. From this vir region fragment four discrete proteins were expressed in minicells. The coding regions were mapped to a part conserved in nopaline and octopine plasmids; in the latter it appears to correspond to vir C/D.