FIG. 3.

Schematic of LR gene and mutants. (A) Locations of the LR gene and ORFs. The 5′ ends of the LR RNA were mapped by RACE (rapid amplification of cDNA ends) PCR or primer extension (3, 21). The vertical lines denote the 5′ termini of the transcripts. In latently infected cattle, the 5′ terminus of LR RNA has additional leader sequences. Splicing of LR RNA (dashed lines) occurs within the region of the transcript that would eliminate the three stop codons of LR ORF2 (8, 21) and may yield transcripts that encode LRP isoforms. The two major ORFs are marked LR ORF 1 and LR ORF 2 (32). The other regions that have the potential to encode a protein (░⃞ and ■) are in reading frames B and C respectively, but do not have a methionine residue at their amino termini. Asterisks indicate where in-frame stop codons are located. (B) Partial restriction map of the 2-kb LR gene. Construction of the mutants is described in Materials and Methods. (C) Locations of the LR primers used to detect LR RNA (21). Sequences of these primers are given in Materials and Methods.