Presence of a Regulatory Element within the First Intron of the Human Platelet‐derived Growth Factor‐A Chain Gene

We detected a suppressive element in the first intron of the human platelet‐derived growth factor A chain (PDGF‐A) gene. Two or more proteins, at least 110‐kd and 90‐kd proteins, were bound over a wide region of this fragment, and the fragment suppressed the expression of the FDGF‐A chain via these proteins in vivo. Since the fragment also had suppressor activity on the promoter of the PDGF‐B chain, it may be involved in a suppressive mechanism of gene expression common to PDGF‐A and ‐B chains. Four tandem repeats of CCCCAT(CCCC) and three direct repeats of GGGGAG were observed in this region. The expression of the PDGF‐A chain is considered to be regulated by a mechanism involving not only the 5’upstream region but also introns.