Cell‐type‐specific expression of mouse DNA polymerase β‐gene is regulated by silencer elements

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Abstract
RNA blot hybridization analysis revealed that the steady‐state level of DNA polymerase β‐mRNA in mouse neuroblastoma N18TG2 cells was approximately fivefold higher than that in NIH/3T3 cells. In order to examine the function of DNA polymerase β‐gene silencers in these two cell lines, we employed a chloramphenicol acetyltransferase (CAT)‐transient expression assay using the CAT plasmids containing the silencers linked to various promoter‐enhancers. In NIH/3T3 cells, DNA polymerase β‐gene silencers effectively repressed the function of its own promoter and those of several other heterologous promoter‐enhancers. In contrast, the silencers only marginally affected the CAT expression directed by DNA polymerase β‐gene promoter and heterologous promoter‐enhancers in N18TG2 cells. The extent of the increase of CAT expression by removing silencer elements in NIH/3T3 cells was very similar to the ratio of DNA polymerase β‐mRNA content in N18TG2 cells to that in NIH/3T3 cells. These results indicate that cell‐type‐specific expression of DNA polymerase β‐gene is primarily controled by the function of its silencer elements.