LC3:PE can be cleaved by ATG4 to release free LC3 (Kirisako et al. 2000, Kabeya et al. 2004, Kumanomidou et al. 2006, Satoo et al. 2009). ATG4 activity can be regulated by reactive oxygen species (ROS) (Scherz-Shouval et al. 2007) possibily to control release of LC3 from closed autophagosomes.