PROGRAMMED FRAMESHIFTING IN THE SYNTHESIS OF MAMMALIAN ANTIZYME IS -2IN BUDDING YEAST(1 IN MAMMALS, PREDOMINANTLY +1 IN FISSION YEAST, BUT)

The coding sequence for mammalian ornithine decarboxylase antizyme is in two different partially overlapping reading frames with no independ ent ribosome entry to the second ORF, Immediately before the stop codo n of the first ORF, a proportion of ribosomes undergo a quadruplet tra nslocation event to shift to the +1 reading frame of the second and ma in ORF, The proportion that frameshifts is dependent on the polyamine level and, because the product antizyme is a negative regulator of int racellular polyamine levers, the frameshifting acts to complete an aut oregulatory circuit by sensing polyamine levels, An mRNA element just 5' of the shift site and a 3' pseudoknot are important for efficient f rameshifting, Previous work has shown that a cassette with the mammali an shift site and associated signals directs efficient shifting in the budding yeast Saccharomyces cerevisiae at the same codon to the corre ct frame, but that the shift is -2 instead of +1, The product contains an extra amino acid corresponding to the shift site. The present work shows efficient frameshifting also occurs in the fission yeast, Schiz osaccharomyces pombe, This frameshifting is 80% +1 and 20% -2. The res ponse of S. pombe translation apparatus to the mammalian antizyme reco ding signals is more similar to that of the mammalian system than to t hat of S, cerevisiae. S. pombe provides a good model system for geneti c studies on the mechanism of at least this type of programmed mammali an frameshifting.