All newly synthesised proteins in the ER are transported through the Golgi from cis cisternae, and are sorted from the trans cisternae and the trans-Golgi network to their final destinations. The mechanism of their passage through the Golgi is of much interest, and one widely accepted model is cisternal maturation, in which proteins are transported by the progression of the cisternae through the Golgi stack. But how cisternal maturation occurs is still unknown. On page 3251, Kazuo Kurokawa, Akihiko Nakano and colleagues examine the function of COPI in cisternal maturation by 4D observation of transmembrane Golgi-resident proteins in living yeast cells. The authors knocked down COPI function using both COPI temperature-sensitive mutants and induced degradation of COPI proteins, and find that inactivation of COPI subunits Ret1 and Sec21 markedly impair the maturation process of cis-to-trans cisternae within the Golgi. In addition, disruption of COPI functions inhibits the dynamic movement of cisternae in the cytoplasm. Taken together, these data further our understanding of the dynamic behaviour of Golgi cisternae in controlling membrane trafficking in yeast.
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