The rat albumin gene promoter is appropriately regulated in transient but not in stable transfections

The tissue-specific expression of the liver-specific rat albumin gene promoter was examined after transfer to various hepatic and non-hepatic cell lines. A 402 base pair sequence from the albumin gene 5 ' flank enabled a fused reporter chloramphenicol acetyltransferase gene to be expressed in rat hepatona cell lines but not in fibroblast lines or dedifferentiated hepatona cells. How-ever, when this same construct was analyzed in permanently transfected cell populations, it was expressed equally well in differentiated and dedifferen-tiated hepatoma cells and in two of three fibroblast lines tested. The inap-propriate expression of the albumin promoter was also seen using the HSV £jj gene and the E. coli gpt gene as reporters, and when assayed by colony forma-tion in HAT medium (£k gene) or by SI protection of transcripts in cotrans-fected populations (£k and gpt genes). These results show that gene regula-tory elements can behave differently in transient vs. stable transfections, and suggest that chromosomal integration can provide long range positive in-fluences on gene expression