J. Biol. Chem., Vol. 265, Issue 16, 9098-9104, 06, 1990
Spatial constraints on polyadenylation signal function
CV Heath, RM Denome and CN Cole
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03756.
Efficient cleavage and polyadenylation of eukaryotic messenger RNAs require
at least two signal elements: an AAUAAA or closely related sequence located
7-30 base pairs (bp) upstream of the site of processing, and a G/U- or
U-rich sequence located 3' to the cleavage site. The herpes simplex virus
type 1 thymidine kinase (tk) gene contains two copies of the AATAAA
hexanucleotide and a GT-rich region. We have shown that the first AATAAA
and the GT-rich region are essential for efficient processing, both in vivo
and in vitro, whereas the second AATAAA does not appear to play any role in
the formation of tk mRNA 3' ends. The failure of a signal containing only
the second AATAAA and the GT-rich element to signal cleavage and
polyadenylation suggested that these two elements might be too close
together to constitute a functional polyadenylation signal. The experiments
described in this report were directed at determining the effects on mRNA
3' end formation of alterations in spacing between signal elements.
Wild-type tk contains 19 bp between these two elements. Constructs were
made in which an AATAAA and the GT-rich region were separated by various
distances ranging from 7 to 43 bp. The quantity and location of 3' ends of
the tk mRNA produced by these constructs in Cos-1 cells were measured by S1
nuclease protection analysis. Signal efficiency was gradually reduced as
the separation between the two signal elements was increased; with a
separation of 43 bp, the signal functioned at approximately one-eighth the
efficiency of the parental construction. Bringing the two signals closer
together resulted in decreased signal efficiency; with a separation of 7 or
9 bp, no tk mRNA polyadenylated within the normal region was produced.
Altering the sequences between these two elements without changing the
distance had small effects on processing efficiency.