Bgs4 absence causes a slower septum formation, uncoupled from an altered and faster CAR contraction. (A and B) WT CAR contraction and PS synthesis are coordinated, whereas Bgs4 absence produces a slower CAR contraction and much slower PS growth. (A) Cells were grown as in Fig. 2 A and imaged by time-lapse. Arrowhead shows first PS signal detected (t = 2), locating in the previous image (t = 0) the simultaneous start of PS synthesis and coupled CAR contraction. (B) The time of CAR assembly, maturation, and contraction and of PS formation was quantified. (C–G) WT CAR contraction and septation are uniform and coincident. In Bgs4 absence, initial CAR contraction and PS formation are strongly impaired (red bracket), but ensuing CAR contraction proceeds faster than in WT and uncoupled from a slower PS formation. (C) Kymographs of the time-lapses of A. (D) Scheme of CAR and PS progression in the kymographs. White arrows show asymmetric septum synthesis start. Arrowhead shows end of CAR contraction (green) and PS formation (blue). Rectangle marks interval (t = 22–26) of growing PS but complete CAR contraction. (E) The slow CAR contraction is coincident with a defective PS synthesis start (arrows). Cells were grown as in A. (F) Detail of defective growing PS uncoupled from complete PM extension. (G) Rates of CAR contraction and PS synthesis (2–6, 6–12, and 12–18 min). Error bars indicate SD. Bars, 1 µm.