McGuire M S, Center M S, Consigli R A
J Biol Chem. 1976 Dec 25;251(24):7746-52.
An endonuclease activity has been purified approximately 800-fold from nuclei of 3T3 cells infected with polyoma virus. The purfied enzyme catalyzes an endonucleoytic cleavage of single- and double-stranded DNA and single-stranded RNA. Evidence that the activity towards these substrates resides in the same protein molecule is provided by the finding that they co-sediment in sucrose gradients and have identical rates of heat inactivation. Studies on the DNase activity shows that the rate of hydrolysis of single-stranded T7 DNA is 100-fold greater than that for double-stranded T7 DNA. Single-stranded DNA is extensively hydrolyzed to low molecular weight acid-insoluble products. With duplex DNA as substrate, only a limited number of single strand breaks are introduced. A limit digest with polyoma DNA (component I) as substrate results in the introduction of four breaks per strand. The phosphdiester bond interruptions can be repaired by polynucleotide ligase. Approximately 80% of the 5' termini present at the point of phosphodiester bond cleavage are purine nucleotides. Additional studies have demonstrated that a similar endonuclease is present in nuclei of uninfected cells and that this enzyme purified 400-fold has catalytic properties identical with those of the endonuclease from infected cells.
一种核酸内切酶活性已从感染多瘤病毒的3T3细胞核中纯化出来，纯化倍数约为800倍。纯化后的酶催化单链和双链DNA以及单链RNA的核酸内切裂解。蔗糖梯度中共沉降以及热失活速率相同的发现，证明了对这些底物的活性存在于同一蛋白质分子中。对DNA酶活性的研究表明，单链T7 DNA的水解速率比双链T7 DNA高100倍。单链DNA被广泛水解为低分子量的酸不溶性产物。以双链DNA为底物时，仅引入有限数量的单链断裂。以多瘤病毒DNA（组分I）为底物进行极限消化，每条链会引入四个断裂。磷酸二酯键的中断可被多核苷酸连接酶修复。在磷酸二酯键断裂处存在的5'末端中，约80%是嘌呤核苷酸。进一步的研究表明，未感染细胞的核中也存在类似的核酸内切酶，这种纯化了400倍的酶具有与感染细胞中的核酸内切酶相同的催化特性。
