Cis effect of lacZ sequences in transgenic mice.

Transgenic mice carrying the 3-hydroxy-3-methylglutarylCoA reductase (HMG) promoter driving the Escherichia coli beta-galactosidase (lacZ) gene did not display the expected ubiquitous and constitutive expression in HMG-lacZ transgenic mice. The same promoter is however able to drive ubiquitous expression of the chloramphenicol acetyltransferase (cat) gene. Two lines of double HMG-lacZ and HMG-cat transgenic mice were obtained in which the two constructs were integrated at the same genomic sites. These mice expressed both reporter genes, but exclusively in the testes. These results suggest that the lacZ sequence might interfere negatively with the expression of the adjacent HMG-cat transgene.