Sensitivity of RAG-1 and RAG-2 PCR assays. RAG-1 and RAG-2 expressing Jurkat cells were serially diluted with phosphate-buffered saline. mRNA was extracted and PCR performed as described in Materials and Methods. The data shown is an autoradiograph after hybridization with RAG-1 and RAG-2 sequence specific probes. Transcripts for both recombinase activating genes (+RT) were detected in two of three replicates from the same sample at the single cell level. The absence of genomic recombinase activating gene sequences was confirmed by amplification of mRNA without prior reverse transcription for the 100-, 10-, and 1-cell dilutions (−RT).