... cells, an O 2 -dependent prolyl 4-hydroxylase (P4H1) required for O-glycosylation of Skp1, a subunit of E3 SCF -Ub-ligases. P4H1-null cells differentiate the basic pre-stalk and pre-spore cell types but exhibit a selectively increased O 2 requirement for culmination, from ∼12% to near or above ambient...