RT-PCR for EBV latent transcripts. RNA samples were subjected to RT reaction, then cDNA was amplified with the appropriate primers for each latent gene region. The PCR products were hybridized to a ³²P-labeled internal oligonucleotide probe. LCL was used as positive control; IBL was used as an additional control because of its similarities to PELs. HL60 is a promyelocytic cell line used as negative control; H₂O represents reactions carried out in the absence of cDNA. The number above each lane corresponds to the PEL case. Diagrams on the left illustrate the corresponding transcripts, with arrows indicating primers and small black squares representing the probes used. β-Actin was used as a control for equal amounts of mRNA used for the RT-PCR reaction.