How does vesicle budding occurs in yeast?Does the vacuoles uses CopI or CopII formation or is there a specific budding mechanism in yeast? Please explain in details. Solution Sec proteins are responsible for vesicle budding. These proteins are present in vesicle named as Cop II. This is a coat protein that makes up the vesicle. Please note that Cop II vesicles bud off proteins from ER towards cis-Golgi, while Cop I vesicles bud off proteins from cis-Golgi to trans-Golgi. The mechanism of budding is similar in yeast; in fact yeast has been used as a model organism for studying vesicular transport and secretory pathway of eukaryotes. Vacuoles also Cop I and Cop II formation..