BACKGROUND&AIM: To explore the influencing factors of nested deletions and find some methods to resolve interrelated problems. MATERIAL AND METHODS: Alkaline lysis,purification by polyethylene glycol(PEG)and QIAprep Spin Miniprep Kit were used to prepare the plasmid pGLB-G6carrying the5'flanking region of NGAL gene to study the nonspecific degradation of Exonuclease(ExoⅢ),the best method of preparing the plasmid,not susceptible to ExoⅢ,would be screened.ExoⅢdeletion reaction was generated at22℃and37℃respect...