Sriprakash K S, Lundh N, Radding C M
J Biol Chem. 1975 Jul 25;250(14):5438-45.
The lambda exonuclease, an enzyme that has been implicated in genetic recombination, rapidly and processively degrades native DNA, starting at the 5' terminus. The enzyme will also degrade the 5'-terminated strand at a single-stranded branch. The experiments reported here reveal various interactions of the enzyme with single-stranded DNA. The rate of digestion is related inversely to the length of single strands. Chains of 100 nucleotides are digested at about 10% the rate of digestion of native DNA. Digestion of the single-stranded ends of lambda DNA does not appear to occur processively. The enzyme binds to circular as well as linear single strands and the affinity for single strands is also related inversely to the chain length. In an equimolar mixture of single- and double-stranded DNA the action of lambda exonuclease on the latteris about half-inhibited. At 20 degrees the initiation of digestion at the 5' terminus of duplex DNA is blocked sterically when such DNA has 3'-terminal single strands that are longer than 100 nucleotides. Information about these properties is important for the practical use of lambda exonuclease as well as for reflections on the role of the enzyme in genetic recombination.
λ核酸外切酶是一种与基因重组有关的酶，它能从5'末端开始快速且持续地降解天然DNA。该酶也会在单链分支处降解5'末端的链。本文报道的实验揭示了该酶与单链DNA的各种相互作用。消化速率与单链长度成反比。100个核苷酸的链被消化的速率约为天然DNA消化速率的10%。λDNA单链末端的消化似乎不是持续进行的。该酶能结合环状和线性单链，对单链的亲和力也与链长成反比。在单链和双链DNA的等摩尔混合物中，λ核酸外切酶对双链DNA的作用约被抑制一半。在20摄氏度时，当双链DNA的3'末端单链长于100个核苷酸时，双链DNA 5'末端的消化起始会在空间上受阻。有关这些特性的信息对于λ核酸外切酶的实际应用以及思考该酶在基因重组中的作用都很重要。
