Chicken calmodulin promoter activity in proliferating and differentiated cells

A 1218-base pair (bp) portion of the chicken calmodulin promoter was sequenced and assayed for promoter activity. This portion of the promoter was found sufficient to produce accurate transcriptional initiation. The promoter sequence was GC rich, particularly in the 700 bp region 5' to the cap site. Eight plasmids were prepared containing the first calmodulin exon and 30-1218 bp of the promoter, ligated to the reporter gene chloramphenicol acetyl transferase. In chicken embryonic fibroblasts and proliferating BC3H-1 cells promoter activity increased progressively with increasing promoter length up to 617 bp. Extension of the promoter beyond 617 bp inhibited expression, as did sequences within the first calmodulin exon. In BC3H-1 cells differentiation was found to reduce calmodulin mRNA levels approximately 3-fold. Activity of the calmodulin promoter constructs also decreased by a similar extent with differentiation. Sequences up to 234 bp 5' to the calmodulin cap site were markedly less effective in elevating chloramphenicol acetyl transferase activity in differentiated BC3H-1 cells than in proliferating cells and may account for the lower overall activity of the calmodulin promoter in these cells. Within this region several sequences were identified, including an extensive homology to the rat calmodulin I gene promoter that could be significant in regulation of calmodulin expression.