Expression and characterization of thymine-DNA glycosylase from Aeropyrum pernix.

The recombinant thymine-DNA glycosylase (TDG) from Aeropyrum pernix (A. pernix) was expressed in Escherichia coli. The enzymatic activity of recombinant A. pernix TDG (ApeTDG) was characterized using oligonucleotides containing a thymine/uracil base as substrate. ApeTDG had distinct glycosylase activity on T/G mismatch. The optimal temperature and pH for thymine removal were 65-70 degrees C and pH 7.0-8.5, respectively. High concentration of NaCl inhibited the thymine removal. Divalent ions had different influence on the thymine removal by ApeTDG. Ca(2+) and Mg(2+) had no inhibition on the enzymic activity, but Ni(2+), Co(2+), Cu(2+), Mn(2+), and Zn(2+) completely inhibited the excision reaction. As derived from a hyperthermophilic archaea, ApeTDG protein was heat-resistant at 75 degrees C. ApeTDG also had a relatively weak DNA glycosylase activity on uracil base, with the following order: U/C>U/G approximately U/T>U/U approximately U/I approximately U/AP approximately U/->U/A. Additional mismatch located at 3' of T/G had less inhibition on the thymine removal than that located at 5' of T/G, and two additional mismatches located at each side of T/G completely inhibited the excision of thymine. Together, these data suggest that ApeTDG is a TDG protein with weak UDG activity.

Avascular osteonecrosis after treatment of SARS: a 3-year longitudinal study.

OBJECTIVE: To investigate the relationship between avascular osteonecrosis (AVN) and corticosteroid treatment given to patients with severe acute respiratory syndrome (SARS). METHODS: Longitudinal study of 71 former SARS patients (mainly health care workers) who had been treated with corticosteroids, with an observation time of 36 months. Magnetic resonance images (MRI) and X-rays of hips, knees, shoulders, ankles and wrists were taken as part of the post-SARS follow-up assessments. RESULTS: Thirty-nine per cent developed AVN of the hips within 3-4 months after starting treatment. Two more cases of hip necrosis were seen after 1 year and another 11 cases of AVN were diagnosed after 3 years, one with hip necrosis and 10 with necrosis in other joints. In total, 58% of the cohort had developed AVN after 3 years of observation. The sole factor explaining AVN in the hip was the total dose of corticosteroids received. CONCLUSION: The use of corticosteroids in SARS has been debated; opinions conflict about whether the immediate benefits in terms of saving lives compensate for the adverse effects, including AVN.