Mammalian cDNA and prokaryotic reporter sequences silence adjacent transgenes in transgenic mice

The ovine beta-lactoglobulin gene is expressed efficiently and at high levels in the mammary gland of transgenic mice. In contrast, when this gene is linked to a second gene construct comprising a mammalian cDNA or a CAT reporter sequence it fails to be expressed in the majority of transgenic lines generated. We suggest that mammalian cDNAs and prokaryotic reporter sequences can serve as active foci for gene silencing in the mammalian genome.