Abstract

Insight into the control of gene expression may be gained by analysing genetic systems marked by both regulatory and structural variants. In such systems one can determine whether a regulatory element controls structural genes on both chromosomes or only on the chromosome to which it is linked. The latter may be detected in individuals heterozygous at both the regulatory and structural loci, in which case the effect of each regulatory allele is seen to be exerted only on the cis-located structural allele. In prokaryotic organisms, the identification of cis interaction of this sort has allowed elucidation of many features of genetic regulation, first for the lac operon and subsequently for a variety of other systems. In higher organisms, however, there have been few opportunities to observe cis-interacting genes. The most thoroughly characterized mammalian system in this regard is the murine beta-glucuronidase locus described by Paigen and his colleagues, in which cis interaction has been shown to occur between two closely linked genetic elements-the beta-glucuronidase structural gene itself and an androgen-activated regulatory gene which controls the quantity of beta-glucuronidase expressed. We report here that cis-interacting genetic elements are also found in the S region of the mouse major histocompatibility complex H-2.