Messenger RNAs transcribed from yeast linear cytoplasmic plasmids possess unconventional 5’ and 3’ UTRs and suggest a novel mechanism of translation

Václav Vopálenský; Michal Sýkora; Tomáš Mašek; Martin Pospíšek

Michael Altman) show a strong drop in protein synthesis (101,102) and a remarkable decrease in the number of polysomes (103) at an elevated temperature. We decided to transfer pGKL plasmids into these strains and determine whether a reasonable amount of the functional pGKL toxin is produced at 37°C, where Cdc33-1 and Cdc33-42 proteins are not functional and translation initiation is thus impaired (101,102). At least three genes (K1ORF2, K1ORF3 and K1ORF4) encoded by the pGKL1 plasmid require sufficient expression in the yeast cells to impart killer and immunity phenotypes. The killer toxin itself is a trimeric protein comprising non-identical alpha, beta and gamma subunits that are encoded by K1ORF2 and K1ORF4 ( Fig. 1) (8,104) . Interestingly, mRNAs transcribed from all three genes belong to the group whose members have the lowest cap occurrence frequency and a high degree of 5' polyadenylation ( Fig. 3C) . The presence of the killer phenotype under restrictive conditions, when cellular cap-dependent translation initiation is disabled, would thus indicate that mRNAs from at least three pGKL genes can be sufficiently and coordinately expressed in a cap-independent manner.