IDENTIFICATION OF 2 CIS-ACTING ELEMENTS THAT INDEPENDENTLY REGULATE THE LENGTH OF POLY(A) ON XENOPUS ALBUMIN PRE-MESSENGER-RNA

Unlike most eukaryotic mRNAs studied to date, Xenopus serum albumin mR NA has a short (17-residue), discrete poly(A) tail. We recently report ed that this short poly(A) tail results from regulation of the length of poly(A) on albumin pre-mRNA, The purpose of the present study was t o locate the cis-acting element responsible for this, the poly(A)limit ing element or PLE, An albumin minigene consisting of albumin cDNA joi ned in exon 13 to the 3' end of the albumin gene produced mRNA with <2 0 nt poly(A) when transfected into mouse fibroblasts. This result indi cates both that cis-acting sequences that regulate poly(A) length are within this construct, and that nuclear regulation of poly(A) length i s conserved between vertebrates, Poly(A) length regulation was retaine d after replacing the terminal 53 bp and 3' flanking region of the alb umin gene with a synthetic polyadenylation element (SPA), Conversely, fusing albumin gene sequence spanning the terminal 53 bp of the albumi n gene and 3' flanking sequence onto the human beta-globin gene yielde d globin mRNA with a 200-residue poly(A)tail. These data indicate that the PLE resides upstream of the sequence elements involved in albumin pre-mRNA 3' processing, Poly(A) length regulation was restored upon f using a segment bearing albumin intron 14, exon 15, and 3' flanking se quence onto the beta-globin gene. We demonstrate that exon 15 contains two PLEs that can act independently to regulate the length of poly(A) .