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

K2ORF4 encodes a putative helicase probably involved in transcription of plasmid-specific mRNAs (18), K2ORF5 codes for a single-stranded DNA-binding protein, and K2ORF10 encodes a protein bound to the terminal inverted repeats of both pGKL plasmids. All these proteins, with the exception of K2Orf3p and K2Orf4p, are probably involved in pGKL1/2 replication (18-22). K2ORF6 and K2ORF7 code for putative subunits of a pGKL1/2-specific RNA polymerase (23, 24) . No function has been assigned to the four remaining ORFs (K2ORF1, 8, 9, and 11) (Fig. 1 ). All ORFs are likely expressed independently. Each gene is preceded by an upstream conserved sequence (UCS) motif, which is located approximately −30 nucleotides from the putative start codon for pGKL1 UCSs (AT A / C TGA) or up to −100 nucleotides in the case of pGKL2 UCSs (ATNTGA) (for review see (2, 18) ). Sequences located between an AUG initiation codon and its respective UCS (inclusive) act as promoters in sensu lato (25) (26) (27) . However, detailed mapping of the promoters recognized by the plasmid-specific RNA polymerase has not been performed.