Cyclin D3 promoter activity is induced by Mpl ligand. A series of 5′-deletions of the cyclin D3 promoter linked to the HGH reporter gene was stably transfected into Y10 cells, which were subsequently cultured in the absence or presence of MGDF as detailed in Materials and Methods. Schematic representation of respective reporter gene constructs is shown adjacent to the presentation of the corresponding HGH levels. The constructs are designated by numbers corresponding to the length of cyclin D3 sequences upstream of the transcriptional start site. The HGH level produced by cells transfected with pD3GH and cultured in the absence of MGDF was designated as 100%. All experiments were normalized for transfection efficiency by cotransfection with pCMVβ-galactosidase, as described in Materials and Methods. The data are the means of four determinations, with standard deviations indicated by the error bars.