Figure 1.

(A) Schematic drawing depicting the organization of the major late transcription unit. Arrows show the relative position of the five families of late mRNAs with the genomic position of the L4-22K and L4-33K marked. (B) Schematic diagram of the MLP showing the position of upstream transcription factor-binding sites (hatched boxes), the first tripartite leader exon (open box), the major late first leader 5΄ splice site (5΄ss), and the L4-22K binding sites in the first leader intron (gray boxes) in relation to the MLP transcription start site (+1). (C) Nucleotide sequence expansion of the R1 region with the L4-22K binding site indicated. (D) Potential hairpin structure of the sense-strand R1 RNA sequence encompassing the L4-22K binding site.