The rate of RNase H cleavage is substantially lower than the rate of DNA synthesis (Kati et al. 1992), so the product of the combined DNA synthesis and RNA degradation events catalyzed by the RT heterodimer mediating minus-strand DNA synthesis is a DNA segment still duplexed with extended viral genomic RNA fragments. Other RT heterodimers bind the remaining RNA:DNA heteroduplexes and their RNase H domains further degrade the viral genomic RNA (Wisniewski et al. 2000a, b). Two PPT (polypurine tract) sequence motifs in the template, one immediately 5' to the U3 sequence and one located within the pol gene in the center of the viral genome, are spared from degradation (Charneau et al. 1992; Julias et al. 2004; Pullen et al. 1993).