A DNASE FROM THE TRYPANOSOMATID CRITHIDIA FASCICULATA

摘要

We have purified to homogeneity a DNase from a Crithidia fasciculata crude mitochondrial lysate, The enzyme is present in two forms, either as a 32 kDa polypeptide or as a multimer containing the 32 kDa polypeptide in association with a 56 kDa polypeptide. Native molecular weight measurements indicate that these forms are a monomer and possibly an alpha(2) beta(2) tetramer, respectively, The monomeric and multimeric forms of the enzyme are similar in their catalytic activities, Both digest double-stranded DNA about twice as efficiently as single-stranded DNA, They introduce single-strand breaks into a supercoiled plasmid but do not efficiently make double-strand breaks, They degrade a linearized plasmid more efficiently than a nicked plasmid, Both enzymes degrade a 5'-P-32-labeled double-stranded oligonucleotide to completion, with the 5'-terminal nucleotide ultimately being released as a 5'-mononucleotide, One difference between the monomeric and multimeric forms of the enzyme, demonstrated by a band shift assay, is that the multimeric form binds tightly to double-stranded DNA, possibly aggregating it.