The current definition of the transfer region comprises the large transfer (tra) operon, the genes traM, traJ, finP and finO as well as the origin of conjugative transfer (oriT). In this study we focus on the function of another gene which also maps outside the tra operon. This gene is encoded by plasmid R1 and was previously sequenced by this laboratory and designated gene 19. It has also been designated "gene X" in plasmid R100 and "ORF169" in plasmid F. Gene 19 is transcribed in the opposite direction to traM and is separated from traM by the oriT. It encodes a polypeptide of 169 amino acids. Expression of gene 19 is controlled posttranscriptionally by RNase III. As part of the so called "leading region" gene 19 is the first gene to be transmitted into the recipient cell during the process of conjugal DNA transfer. Its location and high degree of conservation among F-like suggest an important function of this gene in conjugation, but such a function could not be demonstrated in earlier experiments.
We establish that gene 19 is involved in conjugation as well as bacteriophage infection. On the basis of our observations, we propose to classify gene 19 as a transfer gene, although its exact role in the DNA transfer process still remains to be established. A possible function, suggested by the presence of a conserved motif in protein 19 is the temporally and spatially controlled opening of the peptidoglycan during phage infection and conjugal DNA transfer.
Bayer, M., Eferl, R., Zellnig, G., Teferle, K., Dijkstra, A., Koraimann, G., and G. Högenauer (1995) Gene 19 of plasmid R1 is required both for efficient conjugative DNA transfer and bacteriophage R17 infection. J Bacteriol 177 (15):4279-4288 here is the abstract.