E. Rom et C. Kahana, POLYAMINES REGULATE THE EXPRESSION OF ORNITHINE DECARBOXYLASE ANTIZYME IN-VITRO BY INDUCING RIBOSOMAL FRAME-SHIFTING, Proceedings of the National Academy of Sciences of the United Statesof America, 91(9), 1994, pp. 3959-3963
We provide here an example of a mammalian cellular gene expressed by f
rame-shifting. Conventional reading of the sequence of ornithine decar
boxylase-antizyme mRNA (a protein that modulates the rate of ornithine
decarboxylase degradation) results in premature termination at an in-
frame termination codon (stop-1), located shortly after the initiation
codon. By translating, in vitro in reticulocyte lysate, antizyme mRNA
with a full coding capacity and various mutants derived from it, we d
emonstrate that antizyme expression requires that ribosomes shift from
the first open reading frame (termed ORF(0)) to a second +1 open read
ing frame (ORF(1)). Our studies show that this frame-shifting, which o
ccurs at maximal efficiency of approximate to 20%, is stimulated by po
lyamines and requires the functional integrity of the stop codon (stop
-1) of ORF(0). By introducing in-frame deletions, we have shown that a
n 87-nt segment surrounding stop-1 enhances frame-shifting efficiency,
whereas the 6 nt located just upstream to stop-1 are absolutely essen
tial for this process. Because this segment does not contain sequences
that were previously characterized as shifty segments, our results su
ggest that another mechanism of frame-shifting is involved in mediatin
g antizyme expression.