FIGURE 1.

A, schematic diagram of cap-snatching mechanism in L-A and L-BC viruses. Gag decaps mRNA and forms an intermediate with m⁷Gp through His (His-154 for L-A and His-156 for L-BC). Then m⁷Gp is transferred to the diphosphorylated 5′ end of the emerging viral transcript to form a 5′-5′-triphosphate linkage (cap snatching in cis). m⁷Gp also can be transferred to an externally added viral transcript (cap snatching in trans). B, comparison of selected L-A sequences with those of other fungal totiviruses. His-154 and crucial residues for cap recognition are boxed and indicated by the arrow and vertical bars, respectively. GenBank accession numbers are: L-A (AAA50320.1), TaV1 (ADQ54105.1), XdL1A (NC_020903.1), XdL1B (AFH09413.1), L-BC (NP 042580.1), and SgVL (AGG68772.1)