Biomedical subjects

M E Branum

Publications and source records attributed to M E Branum.

3 recordsLinked to original sources

PubMed2001

DNA repair excision nuclease attacks undamaged DNA. A potential source of spontaneous mutations.

Nucleotide excision repair is a general repair system that eliminates many dissimilar lesions from DNA. In an effort to understand substrate determinants of this repair system, we tested DNAs with minor backbone modifications using the ultrasensitive excision assay. We found that a phosphorothioate and a methylphosphonate were excised with low efficiency. Surprisingly, we also found that fragments of 23-28 nucleotides and of 12-13 nucleotides characteristic of human and Escherichia coli excision repair, respectively, were removed from undamaged DNA at a significant rate. Considering the relative abundance of undamaged DNA in comparison to damaged DNA in the course of the life of an organism, we conclude that, in general, excision from and resynthesis of undamaged DNA may exceed the excision and resynthesis caused by DNA damage. As resynthesis is invariably associated with mutations, we propose that gratuitous repair may be an important source of spontaneous mutations.

Base Sequence↗

PubMed2001

Double-strand hydrolysis of plasmid DNA by dicerium complexes at 37 degrees C.

Significant effort has been made to develop synthetic metal complexes that hydrolyze DNA. Here we report a new dicerium complex, Ce(2)(HXTA) (HXTA = 5-methyl-2-hydroxy-1,3-xylene-alpha,alpha-diamine-N,N,N',N'-tetraacetic acid), which can hydrolyze DNA at pH 8 and 37 degrees C. This complex hydrolyzes DNA restriction fragments to give products with high regioselectivity, affording >90% 5'-OPO(3) and 3'-OH ends, like the products of DNA hydrolyzing enzymes. Ce(2)(HXTA) also hydrolyzes Litmus 29 plasmid DNA to afford both nicked and linear DNA. Analysis of the relative amounts of supercoiled, nicked, and linear DNA present show that there is one double-strand cleavage per ten single-strand cleavages, indicating that the linear DNA formed cannot be the result of two random single-strand cleavage events. The kinetics of nicked and linear DNA formation are comparable, both being associated with apparent first-order rate constants of approximately 1 x 10(-)(4) s(-)(1) for complex concentrations of 10(-)(5)-10(-)(4) M. These observations suggest that similar factors affect the hydrolysis of the first and second DNA strands and that cleaving the phosphodiester bond is likely the rate determining step in both cases. This is the first detailed study of a metal complex shown to mimic DNA hydrolases in their capability to effect double-strand DNA hydrolysis regioselectively at the 3'-O-P bond.

Cerium↗

PubMed1999

Double-strand DNA hydrolysis by dilanthanide complexes.

Although there has been progress in developing artificial hydrolytic DNA cleaving agents, none of these has been shown to carry out the double-strand hydrolysis of DNA. We demonstrate that La(III) or Ce(IV) combined with the ligand 1,3-diamino-2-hydroxypropane-N,N,N', N'-tetraacetate (HPTA) in a 2 : 1 ratio can efficiently cleave supercoiled plasmid DNA at 55 degrees C within a 3-h period. Analysis of end-labeled restriction fragments cleaved by these complexes reveals 3'- and 5'-ends consistent with a hydrolytic mechanism. Unlike for other polydentate carboxylate complexes, plasmid DNA cleavage by La(2)(HPTA) or Ce(2)(HPTA) affords a significant amount of linear DNA with a considerable fraction of the supercoiled form still remaining. This result implies that La(2)(HPTA) and Ce(2)(HPTA) can carry out double-strand cleavage of plasmid DNA. La(2)(HPTA) and Ce(2)(HPTA) represent the first metal complexes demonstrated to be capable of double-strand hydrolytic cleavage of plasmid DNA.

DNA↗