{PDOC00087}
{PS00092; N6_MTASE}
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* N-6 Adenine-specific DNA methylases signature *
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N-6 adenine-specific DNA  methylases (EC 2.1.1.72) (A-Mtase) are  enzymes that
specifically methylate the amino group at the C-6 position of adenines in DNA.
Such enzymes are  found  in the three existing types of bacterial restriction-
modification systems  (in type I system the A-Mtase is the product of the hsdM
gene, and in type III it is the product of the mod gene). All of these enzymes
recognize  a  specific  sequence  in  DNA  and  methylate  an  adenine in that
sequence.

It has been  shown [1,2,3,4] that A-Mtases contain  a conserved motif Asp/Asn-
Pro-Pro-Tyr/Phe in their N-terminal  section,  this conserved  region could be
involved in substrate binding or in the catalytic activity.  We have derived a
pattern from that motif.

-Consensus pattern: [LIVMAC]-[LIVFYWA]-{DYP}-[DN]-P-P-[FYW]
-Sequences known to belong to this class detected by the pattern: ALL,  except
 for m.HhaII where the second Pro is  replaced  by  Gln and in m.HindIII where
 that same Pro is replaced by Tyr.
-Other sequence(s) detected in Swiss-Prot: 33 different proteins that are most
 probably not A-Mtases, and three hypothetical Escherichia coli  proteins that
 could be A-Mtases.

-Note: N-4 cytosine-specific DNA methylases,  which are probably enzymatically
 related to A-Mtases,  also  include  a  conserved  Pro-Pro  dipeptide but the
 residues around them are  sufficiently different to allow the derivation of a
 pattern specific to these enzymes.

-Expert(s) to contact by email:
           Roberts R.J.; roberts@neb.com
           Bickle T.; bickle@ubaclu.unibas.ch

-Last update: December 2004 / Pattern and text revised.

[ 1] Loenen W.A.M., Daniel A.S., Braymer H.D., Murray N.E.
     "Organization and sequence of the hsd genes of Escherichia coli
     K-12."
     J. Mol. Biol. 198:159-170(1987).
     PubMed=3323532
[ 2] Narva K.E., Van Etten J.L., Slatko B.E., Benner J.S.
     "The amino acid sequence of the eukaryotic DNA
     [N6-adenine]methyltransferase, M.CviBIII, has regions of similarity
     with the prokaryotic isoschizomer M.TaqI and other DNA [N6-adenine]
     methyltransferases."
     Gene 74:253-259(1988).
     PubMed=3248728
[ 3] Lauster R.
     "Evolution of type II DNA methyltransferases. A gene duplication
     model."
     J. Mol. Biol. 206:313-321(1989).
     PubMed=2541254
[ 4] Timinskas A., Butkus V., Janulaitis A.
     "Sequence motifs characteristic for DNA [cytosine-N4] and DNA
     [adenine-N6] methyltransferases. Classification of all DNA
     methyltransferases."
     Gene 157:3-11(1995).
     PubMed=7607512

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