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.