T. Humphrey et al., RNA 3' END SIGNALS OF THE S-POMBE URA4 GENE COMPRISE A SITE DETERMINING AND EFFICIENCY ELEMENT, EMBO journal, 13(10), 1994, pp. 2441-2451
We have defined sequences in the 3' non-coding region of the Schizosac
charomyces pombe ura4 gene that are required for efficient mRNA 3' end
formation. Three separate sequence elements have been identified. Two
of these are site determining elements which specify alternative site
s of polyadenylation [the major poly(A) site and a minor downstream po
ly(A) site]. The third sequence, located downstream of both poly(A) si
tes, functions as an efficiency element that enhances utilization of e
ither polyadenylation site. By employing sensitive RT-PCR analysis, we
demonstrate that although low levels of transcripts are detected up t
o the efficiency element, none is detected beyond this point. The down
stream site determining element and efficiency element have both been
delineated to specific 16 nt sequences which we show are together suff
icient for ura4 mRNA 3' end formation. We have further characterized t
he interaction between these two elements and show that the efficiency
element behaves in a position-independent, orientation-dependent mann
er, but cannot form 3' ends independently of the site determining elem
ent. Surprisingly, we find that the efficiency element can be function
ally replaced by a second copy of either site determining element. We
present a model for the mechanism of RNA 3' end formation of the ural
gene and note that this bipartite structure for a poly(A) signal in S.
pombe may be related to the AAUAAA and downstream GU-rich sequences of
poly(A) signals in mammalian genes.