Enhancing the efficiency of transgene expression.

Two strategies for enhancing gene expression in transgenic animals are described with particular reference to targeting expression to the mammary gland. Gene constructs in which the protein-encoding DNA sequences are contained within a genomic segment (comprising most or all of the natural introns of the corresponding gene) are shown to be expressed more efficiently than their intronless counterparts. Secondly, co-integrating an otherwise poorly expressed transgene in the vicinity of an actively expressed transgene can dramatically improve its efficiency of expression.