FIG. 3.

Southern blot analysis of ΔMo+SRS M-MuLV-induced tumors. High-molecular-weight DNAs from ΔMo+SRS M-MuLV-induced tumors were digested with PstI, which cleaves asymmetrically within the SRS enhancer fragment. (A) Hybridization with a labeled SRS enhancer-specific probe would yield a diagnostic 839-bp hybridizing fragment for ΔMo+SRS⁺ M-MuLV and a 757-bp fragment for ΔMo+SRS⁻ M-MuLV. (B) Southern blots of the tumors all show fragments of the expected size when hybridized with an SRS 19-6 MuLV enhancer probe. Larger hybridizing fragments presumably represent endogenous MuLV sequences (also present in control spleen DNA) or host-virus junction fragments from the downstream LTR.