FAQ: What is the difference between DNase I (RNase-free) (NEB #M0303) and DNase I-XT (NEB #M0570)?

DNase I (NEB #M0303) is inhibited by salt concentrations >50 mM.  DNase I-XT is a salt-tolerant DNase I which retains activity up to 300 mM salt, but with optimal activity at salt concentrations between 50-100 mM. DNase I-XT is therefore the preferred enzyme for DNA template removal from an in vitro transcription (IVT) reaction. 

Moreover, while the unit definitions of DNase I (RNase-free) and DNase I-XT differ in various contexts (including temperature, substrate and buffer conditions), 1 unit of DNase I-XT (NEB #M0570) is equivalent to 1 unit of DNase I (RNase-free) (NEB #M0303).