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Novel m4C modification in type I restriction-modification systems.

Richard D Morgan1, Yvette A Luyten2, Samuel A Johnson2

  • 1New England Biolabs, 240 County Road, Ipswich, MA 01938, USA morgan@neb.com.

Nucleic Acids Research
|September 2, 2016
PubMed
Summary
This summary is machine-generated.

Researchers discovered a new Type I Restriction-Modification enzyme subgroup that protects hosts by modifying DNA. These enzymes create a novel m4C modification, differing from previously known m6A modifications in Type I systems.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Type I Restriction-Modification (RM) enzymes are crucial for host protection against foreign DNA.
  • Existing Type I RM systems typically involve identical methyltransferase (MTase) subunits and modify adenine to m6A.
  • The evolutionary origins and functional diversity of RM enzymes are areas of ongoing research.

Purpose of the Study:

  • To identify and characterize novel subgroups of Type I Restriction-Modification enzymes.
  • To elucidate the DNA modification specificities and subunit composition of these new enzyme systems.
  • To investigate the evolutionary relationship between newly identified and previously known Type I RM enzymes.

Main Methods:

  • SMRT sequencing was employed to determine the DNA recognition specificity of ten novel Type I RM systems.
  • Biochemical analysis was used to characterize the methyltransferase (MTase) subunits and their catalytic motifs.
  • Comparative sequence analysis was performed to infer evolutionary relationships.

Main Results:

  • A new subgroup of Type I RM enzymes was identified, characterized by a heterodimeric M1M2S MTase structure.
  • These enzymes exhibit novel DNA modification capabilities, producing 4-methylcytosine (m4C) on one DNA strand and adenine (m6A) on the opposite strand.
  • Ten distinct DNA sequence motifs recognized by these novel systems were determined.
  • MTase subunits were classified into two families based on conserved catalytic motif IV (NPPF for m6A, NPPY for m4C).

Conclusions:

  • The newly identified Type I RM enzymes represent the first instances of m4C modification within this enzyme class.
  • These m4C-producing systems likely evolved recently from common m6A Type I systems through the replacement of adenine-targeting domains with cytosine-recognizing domains.
  • The discovery expands our understanding of DNA modification diversity and the evolutionary plasticity of RM enzymes.