ER trapping reveals Golgi enzymes continually revisit the ER through a recycling pathway that controls Golgi organization

Using a rapamycin-based, endoplasmic reticulum (ER) trapping scheme, modified to avoid the problem of an endogenous ER-localized FKBP-binding protein, we demonstrate that Golgi enzymes constitutively recycle back to the ER and that such recycling plays a central role in the maintenance, biogenesis, and inheritance of the Golgi apparatus in mammalian cells. We describe morphological characteristics of the retrograde carriers that ferry Golgi enzymes back to the ER and identify key molecular machinery regulating carrier formation. The study helps resolve the long-standing debate regarding the extent of Golgi enzyme trafficking back to the ER, paving the way for further investigations into the mechanistic details and functional implications of the Golgi's steady-state existence and relationship to the ER.