Journal of Molecular Biology
Volume 252, Issue 3, 22 September 1995, Pages 289-295
Journal home page for Journal of Molecular Biology

Kinetics of Expression of Inducible β-Galactosidase in Murine Fibroblasts: High Initial Rate Compared to Steady-state Expression

https://doi.org/10.1006/jmbi.1995.0496Get rights and content

Abstract

We have constructed a murine fibroblast cell line in which synthesis of β-galactosidase can be induced by incubation with isopropyl-β-d- thiogalactopyranoside (IPTG). This was obtained by transfection by both a plasmid expressinglacIand a second plasmid expressinglacZfrom a modified simian virus 40 (SV40) promoter containing alacoperator. We have measured the induction kinetics as well as the basal and induced differential rate of synthesis of β-galactosidase. The steady-state rate of synthesis is tenfold higher in the presence than in the absence of inducer; we calculate an average of 1200lacZpolypeptides are synthesized per minute per cell in the induced cultures. However, immediately after induction, the rate of accumulation of β-galactosidase is up to 50-fold higher than the basal level. Based on our measurements of stability of β-galactosidase, we suggest that induction may result in a subsequent down-modulation of the transcriptional activity from the induced gene. We hypothesize this inhibition may result from structural changes in DNA components, such as nucleosomes.

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