Nucleic Acids Research, Vol 25, Issue 5 987-991, Copyright © 1997 by Oxford University Press
DR Mernagh, LA Reynolds and GG Kneale
The type I DNA methyltransferase M.EcoR124I consists of two methylation
subunits (HsdM) and one DNA recognition subunit (HsdS). When expressed
independently, HsdS is insoluble, but this subunit can be obtained in
soluble form as a GST fusion protein. We show that the HsdS subunit, even
as a fusion protein, is unable to form a discrete complex with its DNA
recognition sequence. When HsdM is added to the HsdS fusion protein,
discrete complexes are formed but these are unable to methylate DNA. The
two complexes formed correspond to species with one or two copies of the
HsdM subunit, indicating that blocking the N- terminus of HsdS affects one
of the HsdM binding sites. However, removal of the GST moiety from such
complexes results in tight and specific DNA binding and restores full
methylation activity. The results clearly demonstrate the importance of the
HsdM subunit for DNA binding, in addition to its catalytic role in the
methyltransferase reaction.
ARTICLES
DNA binding and subunit interactions in the type I methyltransferase M.EcoR124I
Biophysics Laboratories, School of Biological Sciences, University of Portsmouth, St Michael's Building, Portsmouth PO1 2DT, UK.
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