Abstract: The invention relates to a process for the removal of selectable marker gene sequences, in particular antibiotic gene sequences, from nucleic acid molecules. The invention further relates to the application of this process in the unlabelled integration and deletion of chromosomal genes and in controlling gene expression.

Abstract: The invention relates to a system for stable maintenance of a plasmid, to host cells for use in this system and to methods of using the system to obtain a plasmid useful in medical applications. In particular, the invention provides transformed host cell containing: i) a chromosomal gene which inhibits cell growth; and ii) a plasmid encoding an antisense sequence, wherein the antisense sequence encoded by the plasmid inhibits the action of the chromosomal gene, thereby permitting cell growth and a method for stable maintenance of a plasmid in a host cell in vivo.

Abstract: The invention relates to a process for the removal of selectable marker gene sequences, in particular antibiotic gene sequences, from nucleic acid molecules. The invention further relates to the application of this process in the unlabelled integration and deletion of chromosomal genes and in controlling gene expression.

Abstract: The invention relates to a system for stable maintenance of a plasmid, to host cells for use in this system and to methods of using the system to obtain a plasmid useful in medical applications. In particular, the invention provides transformed host cell containing: i) a chromosomal gene which inhibits cell growth; and ii) a plasmid encoding an antisense sequence, wherein the antisense sequence encoded by the plasmid inhibits the action of the chromosomal gene, thereby permitting cell growth and a method for stable maintenance of a plasmid in a host cell in vivo.

Abstract: The invention relates to host cells and methods of preparing a substantially RNA-free cellular component, comprising culturing cells producing the cellular component in a medium and lysing the cells to produce a cell lysate, wherein the cell lysate contains the cellular component and sufficient RNase activity to degrade substantially all of the RNA molecules present in the cell lysate. The invention also relates to substantially RNA-free cellular components.

Abstract: A system is described which utilizes a novel system of repressor titration for maintenance of a plasmid useful in gene therapy and production of a recombinant protein. The system utilizes a transformed host cell containing a plasmid including an operator susceptible to binding by a repressor expressed in trans, a first chromosomal gene encoding the repressor, and a second chromosomal gene that is functionally associated with an operator and essential for cell growth, wherein the plasmid is present in the cell in sufficient numbers to titrate the repressor such that the essential gene is expressed, thereby permitting cell growth.