Several mechanisms regarding activation of c-myc have been proposed. However, the molecular mechanism by which c-myc deregulation can occur remains obscure and no supparting evidence for a clearly defined regulation of c-myc expression has been provided. This research was designed to investigate the possible effect of exon 1 and its upstream sequences on c-myc expression. The transcriptional activities of exogenous plasmids and endogenous c-myc were studied for their expression after NIH3T3 cells were transiently transfected with plasmids containing exon 1 and upstream sequences of mouse c-myc that are putativelv regulatory sequences. The results of this research rule out a possible role of putatively regulatory sequences for transacting elements, an activator and a repressor, because the expressions of c-myc were not affected by the exogenous elements of exon 1 or upstream sequence in NIH3T3 fibroblast cells.