A MOLECULAR ANALYSIS OF A BROAD-HOST-RANGE PLASMID ISOLATED FROM THIOBACILLUS-FERROOXIDANS

A 12.4-kb plasmid, pTF-FC2, that was isolated from Thiobacillus ferroo xidans and which is capable of replication in a wide range of Gram-neg ative bacteria, has been sequenced. The extent of the regions involved in both replication and mobilization have been delineated. The site o f initiation of replication (oriV) has been localized on a 185-bp frag ment and the origin of transfer (oriT) on a 138-bp fragment. Three pro teins that were essential for replication and four that were essential for mobilization have been identified. The origin of replication was clearly similar to that of the IncQ plasmids although no complementati on or incompatibility between pTF-FC2 and the IncQ plasmid, R300B, was detected. There was a clear similarity in the size, location and amin o acid sequence of the proteins of the pTF-FC2 mobilization region wit h those of the Tral region of the IncP plasmids, RP4 and R751. Two inv erted repeated sequences which had 37/38-bp and 38/38-bp sequence iden tity with the Tn21 transposon were identified. The C-terminal part of a transposase and the N-terminal portion of a resolvase were located b etween the inverted repeats. These open reading frames are most likely the remnants of a defective transposon. A protein with homology to a mercury-resistance regulator was also present within the transposon-li ke element although no gene encoding for mercury reductase could be in dentified.