Background: RecJ

a highly conserved protein in archaea and bacterium

is a single-stranded DNA（ssDNA）-specific 5 to 3 exonuclease that plays an important role in homologous recombination

base excision repair（BER） and methyl directed mismatch repair（MMR）.And RecJ could degrade single-stranded RNA（ssRNA） from 3 to 5 specially.Purpose: RecJ from pyrococcus furiosus was expressed

purified and crystallized.The aim is to get the structure of the protein

clarify the functions of RecJ in cells and to investigate its effect on the degradation of different nucleotide substrates（DNA/RNA）.Methods: In order to get the crystal of RecJ

E.coli was chosed to express the protein.And the protein was purified by metal-chelating chromatography and anion exchange chromatography.The crystal was obtained by screening and the crystal with better diffraction was got by optimization.The data was collected from beamline BL17U1 at SSRF.Results and conclusions: The crystal of P.fu RecJ was got by screening

but the structure has not been achieved because of the low resolution of crystal.