Progressive induction of beta-glucuronidase in individual kidney epithelial cells.

The magnitude and kinetics of beta-glucuronidase induction in mouse kidney are determined by a cis-acting regulatory gene, Gus-r, that is closely linked to the enzyme structural gene. The accumulation of beta-glucuronidase mRNA during induction is much slower than the turnover time of the mRNA, suggesting progressive acquisition of mRNA synthesizing capacity during induction. Counts of the numbers of induced cells present at various times of induction in strains carrying three different alleles of Gus-r show that all potentially responsive cells respond immediately. The level of induction is progressive in individual cells and does not involve continued recruitment of new cells into the induced population. It appears that during induction each chromosome becomes progressively more active in directing the synthesis of beta-glucuronidase.