Lm. Golightly et al., 3 ' UTR elements enhance expression of Pgs28, an ookinete protein of Plasmodium gallinaceum, MOL BIOCH P, 105(1), 2000, pp. 61-70
In Plasmodium parasites the fusion of gametes to form a fertilized zygote a
nd morphogenesis into the motile ookinete are critical developmental stages
in the parasite's complex life cycle. In analogous developmental stages of
metazoan organisms 3' gene flanking regions are critical in the regulation
of gene expression. To determine whether these mechanisms;are conserved in
the protozoan parasite we studied the 3' gene flanking elements necessary
for the expression of Pgs28, the major surface protein of mature zygotes an
d ookinetes of the chicken malaria Plasmodium gallinaceum. The DNA sequence
of the pgs28 3' gene flanking region contains 7 eukaryotic polyadenylation
consensus signals (AATAAA/ATTAAA). An unusual 82% T-rich region is located
55 nucleotides upstream of the fifth polyadenylation signal (ATTAAA). The
pgs28 mRNA terminates approximately 20 nucleotides from the polyadenylation
signal in a poly (A) tail. To determine whether the T-rich region and poly
adenylation signals were necessary for Pgs28 protein expression, sexual sta
ge parasites were transfected with plasmids containing deletions of these e
lements utilizing firefly luciferase (LUC) and beta-glucuronidase (GUS) as
markers of transient gene transfection. The parasites were allowed to devel
op in vitro to the ookinete stage and assayed for enzymatic activity. Cells
transfected with plasmids containing deletions of the T-rich region or fif
th eukaryotic polyadenylation consensus signal expressed 89 and 92% less en
zymatic activity respectively than those transfected with the full length p
gs28 3' gene flanking region. The U-rich element and fifth eukaryotic polya
denylation consensus sequence within the pgs28 3' UTR are therefore necessa
ry for Pgs28 protein expression. (C) 2000 Published by Elsevier Science B.V
. All rights reserved.