The Long Terminal Repeat of Moloney Sarcoma Provirus

Retroviruses are RNA viruses that replicate through DNA intermediates (Temin 1976), and an obligatory step in their life cycle is integration of a DNA interme-diate into the host genome (Temin and Baltimore 1972; Varmus et al. 1973). Structural analyses of both inte-grated and unintegrated proviral DNA have shown that both have directly repeated terminal sequences (Hughes et al. 1978; Sabran et al. 1979). These sequences, called long terminal repeats (LTR), are at he molecular ends of integrated provirus and form junctions with host se-quences, suggesting a gration. The steps leading to retrovirus replication (Gilboa et al. 1979a,b;