Celltech Limited

Edwina M Wright

Geoffrey Thomas Yarranton

Gwynfor O Humphreys

Celia A Caulcott

Martin K Robinson

A new class of DNA vectors, each comprising two replication systems; a first origin of replication resulting in a low copy number and stable inheritance of the plasmid, and a second, high copy number, origin of replication at which replication is directly controllable such that, when host cells carrying the vector are propagated under a first set of conditions, replication takes mainly from the low copy number origin, and that when said cells are propagated under a second set of conditions, replication takes place also from the high copy number origin to produce a high yield of gene product. The controllable origin of replication may be under the control of a natural promoter of RNA transcription or a substitute promoter such as the PL promoter or lac promoter.

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Taplow, United Kingdom

Edwina M Wright