Cell and Molecular Biology of DNA Methyltransferase 1 - International Review of Cell and Molecular Biology - page 12

Figure 1.4 Symmetric cytosine methyltransferases (maintenance methyltransferases).
Comparisons of amino acid domains of plant and animal maintenance methyl-
transferase enzymes. Vertebrate DNMT1 enzymes are very similar to each other in
almost all aspects, whereas the Arabidopsis MET1 CpG maintenance methyltransferase
shows minimal similarity to vertebrate DNMT1 enzymes outside the highly conserved
catalytic domain. Comparison of mouse and chicken DNMT1 sequences shows near
identity except in a region embedded in the large intrinsically disordered domain of
DNMT1. DMAP, known DMAP1 interaction domain; DOD, intrinsically disordered
domain; RFTS, replication focus targeting sequence; CR, cysteine-rich region; BAH1
and BAH2, bromo-adjacent homology domains.
these regions are unique to each protein (not found in proteins other than
MET1 and DNMT1), suggesting that they are involved in functions that
are different between the two proteins. Taken further, this might
suggest that CpG methylation is regulated in very different ways in
A. thaliana (MET-dependent methylation) compared to mammalian species
(DNMT1-dependent methylation). Distinct areas of this region of DNMT1
are particularly interesting, as they have been implicated in biological func-
tions of the protein, primarily through the study of physical interactions with
other biologically relevant proteins and through genetic studies in cells and
model vertebrate organisms. The positions of most of these regions are shown
in Fig. 1.4 . These regions include a DMAP1-interaction domain ( Rountree
et al., 2000 ), a conserved PCNA-binding motif ( Chuang et al., 1997 ), a large
contiguous disordered domain that evolutionarily has expanded in size dur-
ing vertebrate evolution ( Borowczyk et al., 2009 ), and different nuclear
localization sequences ( Cardoso and Leonhardt, 1999 ). Known and many