Li C J, Hwa K Y, Englund P T
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Nucleic Acids Res. 1995 Nov 11;23(21):4426-33.
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 nickel plasmid. Both enzymes degrade a 5'-32P-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.
我们已从粗制的克氏锥虫线粒体裂解物中纯化出一种核酸酶，使其达到同质状态。该酶以两种形式存在，一种是32 kDa的多肽，另一种是包含32 kDa多肽与56 kDa多肽结合的多聚体。天然分子量测量表明，这些形式分别是单体，可能是α2β2四聚体。该酶的单体和多聚体形式在催化活性方面相似。两者消化双链DNA的效率约为单链DNA的两倍。它们将单链断裂引入超螺旋质粒，但不能有效地产生双链断裂。它们降解线性化质粒比镍质粒更有效。两种酶都能将5'-32P标记的双链寡核苷酸完全降解，5'-末端核苷酸最终以5'-单核苷酸形式释放。通过带移分析证明，该酶的单体和多聚体形式之间的一个区别是，多聚体形式紧密结合双链DNA，可能使其聚集。
