REGULATED NUCLEAR POLYADENYLATION OF XENOPUS ALBUMIN PRE-MESSENGER-RNA

Cytoplasmic regulation of the length of poly(A) on mRNA is a well-char acterized process involved in translational control during development . In contrast, there is no direct in vivo evidence for regulation of t he length of poly(A) added during nuclear pre-mRNA processing in somat ic cells. We previously reported that Xenopus serum albumin [Schoenber g ef al, (1989) Mel. Endocrinol, 3, 805-815] and transferrin [Pastori et at (1992) J. Steroid Biochem, Mob Biol. 42, 649-657], mRNA have exc eptionally short poly(A) tails ranging from 12 to 17 residues, whereas vitellogenin mRNA has long poly(A), An RT-PCR protocol was adapted to determine the length of poly(A) added onto pre-mRNA, defined here as that species bearing the terminal intron. Using this assay we show tha t vitellogenin pre-mRNA has the same long poly(A) tail as mature vitel logenin mRNA, In contrast, albumin pre-mRNA has the same short poly(A) as found on fully-processed albumin mRNA, These results indicate that the short poly(A) tail on albumin mRNA results from regulation of pol y(A) addition during nuclear 3' processing.