| 摘要 |
Streptomycete host cells having reduced restriction activity are obtd. by (a) mutagenesis of a strain of streptomycete species to provide host cells of differing genetic characteristics; (b) growth of the surviving host cells and form-ation of protoplasts; (c) transformation of the protoplasts with plasmid DNA from another source. This plasmid DNA contains an origin of replication and a selective marker for the streptomycete host, as well as any DNA sequences necessary for replication and selective culture from the other source; (d) regeneration of host cells from these protoplasts; (e) selection of host cells that have received the plasmid DNA and have been unable to restrict it, by selecting for expression of the selective marker; (f) confirm-ation that the host cells have reduced restriction activity; and (g) if desired, repetition of steps (a)-(f) to reduce further the restriction activity of the host cells and to confirm their further reduced restriction activity.
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