Cloning and sequencing of restriction fragments generated by Eco RI*

Thirty-four Eco RI* sites have been identified on the nucleotide sequence of CaMV, following cloning of Eco RI* fragments in M13mp2. From this sequencing data, we have deduced that Eco RI* recognizes sites that differ in a single position from the canonical Eco RI sequence, GAATTC. Any substitution can occur at any one of the six positions in the recognition site, with the exception of A leads to T or T leads to A changes within the central tetramer. The Eco RI* restriction patterns of phi x174 and pBR322 are consistent with these recognition criteria. Similarly, Bam HI* cleavage of phi x174 and SV40 (George et al., 1980) produces restriction patterns that are consistent with single-position degeneracy in the canonical Bam HI recognition site. Cohesive termini produced by Eco RI* cleavage were ligated into the Eco RI site of M13mp2, even when there was a base pair mismatch within the four nucleotide overlap. Mismatches were corrected asymmetrically during subsequent replication of M13 in E. coli.