|
Three proteins, two DNA methylases and an endonuclease, from the DpnII
restriction system of Streptococcus pneumoniae recognize the DNA sequence 5'
GATC 3' but have very different amino acid sequences, which make them
interesting subjects for structural determination. A purification procedure was
developed that conveniently yields milligram amounts of the DpnM methylase. The
DpnM protein tends to precipitate at reduced ionic strength, and this property
was exploited to yield well-formed bipyramidal crystals. By X-ray diffraction,
the crystals of DpnM were found to be orthorhombic, with cell dimensions a =
56.9 A, b = 68.2 A, c = 84.5 A; systematic absences identify the space group as
P2(1)2(1)2(1). Diffraction extends beyond 3 A, so the crystals may allow
structural determination at atomic resolution.
|
