Kluyveromyces lactisKiller Plasmid pGKL2: Evidence for a Viral-like Capping Enzyme Encoded by ORF3

ORF3 of the cytoplasmic linear plasmid pGKL2 was disruptedin vivoby integration of a selectable marker. Long-term cultivation of transformants carrying hybrid plasmids with a disrupted ORF3 under selective pressure did not deprive strains of the native counterpart, thereby proving its essentiality for pGKL2 replication and maintenance. The predicted ORF3 polypeptide was found to contain conserved motifs acquainted with mRNA-capping enzymes in the required order, just as in cytoplasmic viruses; new conserved motifs were also identified.