| 摘要 |
DNA vectors belonging to a previously unknown group have two replication systems each, namely a first replication starting site, which results in a low copy number and stable hereditary characteristics for the plasmid, and a second replication starting site, which gives a high copy number. The replication is directly controllable, so that when some host cells carrying vectors are propagated under a first set of conditions, replication mainly takes place from the starting site that gives a low copy number, while the propagation of the cells under a second set of conditions gives rise to replication from the starting site that leads to a high copy number, so that the gene product is obtained in a high yield. The controllable replication starting sites can be under the regulation of either a natural promoter for RNA transcription or a substitute promoter such as a PL promoter or a lac promoter. <IMAGE> |
