FIG. 3.

Alignment of U3 sequences of polytropic MLV-related proviruses. Sequences of polytropic MLV-related U3 regions cloned from M. musculus and M. spretus DNAs as described in the previous legend are aligned with those of polytropic (MX27) and modified polytropic (MX33) proviruses (49). The MX27 sequence was used as a standard. Dots indicate nucleotide identity. Dashes indicate absence of a nucleotide. Direct repeats and unique sequences present in the proviruses are boxed (55). The 190-bp inserted region is also boxed. Potential enhancer sequence regions are indicated by the shaded bar. Locations of two promoter-associated motifs, the CAT and TATA boxes, are also indicated. The sequences of oligonucleotide probes are underlined. The conserved PstI recognition site is also shown. The size of the U3 region of each provirus is indicated at the end of the sequence in parentheses.