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

Saha et al. used the latter approach to show that the methyltransferase domain of the vaccinia virus capping enzyme, which is composed of the co-expressed catalytic C-terminal part of D1 and stimulatory D12 subunits, can function in lieu of the yeast cap methyltransferase Abd1 (64) . A similar approach was also used to test the N 7 methyltransferase activities of viral capping enzymes (65, 66) . On the other hand, some cap methyltransferases, including Hcm1 (from human), do not require any auxiliary factors to be co-expressed to support yeast growth in lieu of the Abd1 protein (54, 58, 66) . We should notice that the vaccinia virus D1 protein itself displays mild MTase activity (48), and we complemented the temperature-sensitive phenotype, allowing us to follow the yet unobserved complementation of a partial loss of Abd1 activity in cells. Another, and perhaps the most likely, explanation why K2Orf3p does not complement the mRNA capping machinery in yeast temperature-sensitive mutants is based on the recent observation that expression of AT-rich pGKL genes in yeast nuclei does not lead to functional products due to the frequent premature 3' polyadenylation of the resulting mRNAs (67) .