Cloning, Purification and Initial Characterization of E. coli McrA, a Putative 5-methylcytosine-specific Nuclease
Expression strains of Escherichia coli BL21(DE3) overproducing the E. coli m5C McrA restriction protein were produced by cloning the mcrA coding sequence behind a T7 promoter. The recombinant mcrA minus BL21(DE3) host produces active McrA as evidenced by its acquired ability to selectively restrict the growth of T7 phage containing DNA methylated in vitro by HpaII methylase. The mcrA coding region contains several non-optimal E. coli triplets. Addition of the pACYC-RIL tRNA encoding plasmid to the BL21(DE3) host increased the yield of recombinant McrA (rMcrA) upon induction about 5- to 10-fold. McrA protein expressed at 37 C is insoluble but a significant fraction is recovered as soluble protein after autoinduction at 20 C. rMcrA protein, which is predicted to contain a Cys4-Zn2+ finger and a catalytically important histidine triad in its putative nuclease domain, binds to several metal chelate resins without addition of a poly-histidine affinity tag. This feature was used to develop an efficient protocol for the rapid purification of nearly homogeneous rMcrA. The native protein is a dimer with a high a-helical content as measured by circular dichroism analysis. Under all conditions tested purified rMcrA does not have measurable nuclease activity on HpaII methylated (Cm5CGG) DNA, although the purified protein does specifically bind HpaII methylated DNA. These results have implications for understanding the in vivo activity of McrA in 'restricting' m5C-containing DNA and suggest that rMcrA may have utility as a reagent for affinity purification of DNA fragments containing m5C residues.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 959958
- Report Number(s):
- BNL-82944-2009-JA; TRN: US201016%%1102
- Journal Information:
- Protein Expression and Purification, Vol. 62
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
AFFINITY
CHELATES
CLONING
DICHROISM
DIMERS
DNA
ESCHERICHIA COLI
FINGERS
HISTIDINE
IN VITRO
IN VIVO
INDUCTION
NUCLEASES
PLASMIDS
PROTEINS
PURIFICATION
RESIDUES
RESINS
STRAINS
TRIPLETS
national synchrotron light source