Dnmt1 interactions between N- and C-terminal domains. A. Overview of the general organization of the five DNA methyltransferase family members. Some of the functional domains or structural motifs recognized in the N-terminus of Dnmt1 and Dnmt3 include a PCNA binding domain (PBD), a targeting sequence (TS), a cysteine-rich region (C), a polybromo homology domain (PBHD), a tryptophan-rich region (PWWP) and another cysteine-rich region (C-rich). The vertical bars inside the C-terminus correspond to the highly conserved motifs found in most DNA methyltransferases. For simplicity, only motifs I, IV and X are labeled. The linker region – a (GlyLys)6 repeat – between the N- and C-terminus of Dnmt1 is represented by a short thick horizontal line. B. A series of N- and C-terminal deletions of Dnmt1 were tested for interaction with their corresponding full-length terminal domain. The full-length N-terminus and the first two deletion constructs were generated by PCR amplification and inserted into pBTM117c.1 (lines 1–3, see Methods). The full-length construct was used to derive several deletions using the restriction enzymes NheI (line 5), NcoI (line 6), and BspEI (line 8). The full-length N-terminus was also cloned into pACT2 from which two deletions were derived using the enzyme BglII (lines 4, 7). The N-constructs 1, 2, 3, 5, 6 and 8 were tested as baits for interaction with the C-terminus whereas the N-constructs 1, 4 and 7 were tested as prey with the C-terminus. The C-terminus construct was obtained by digestion with EcoRI (line 9). The interaction was scored using two reporters, lacZ and HIS3 (see Methods). Each member of a pair showing interaction was tested singly to rule out autoactivation. Duplicate results are separated by a slash (/).