DNA methylation patterns in genome are maintained during replication by a DNA 
methyltransferase Dnmt1. Mouse Dnmt1 is a 180 kDa protein comprising the 
N-terminal regulatory domain, which covers 2/3 of the molecule, and the rest 
C-terminal catalytic domain. In the present study, we demonstrated that the 
limited digestion of full-length Dnmt1 with different proteases produced a 
common N-terminal fragment, which migrated along with Dnmt1 (1-248) in 
SDS-polyacrylamide gel electrophoresis. Digestion of the N-terminal domains 
larger than Dnmt1 (1-248) with chymotrypsin again produced the fragment 
identical to the size of Dnmt1 (1-248). These results indicate that the 
N-terminal domain of 1-248 forms an independent domain. This N-terminal domain 
showed DNA binding activity, and the responsible sequence was narrowed to the 79 
amino acid residues involving the proliferating cell nuclear antigen (PCNA) 
binding motif. The DNA binding activity did not distinguish between DNA 
methylated and non-methylated states, but preferred to bind to the minor groove 
of AT-rich sequence. The DNA binding activity of the N-terminal domain competed 
with the PCNA binding. We propose that DNA binding activity of the N-terminal 
domain contributes to the localization of Dnmt1 to AT-rich sequence such as Line 
1, satellite, and the promoter of tissue-specific silent genes.