BNI4 encodes a scaffold protein that tethers chitin synthase III (Chs3p) to the bud neck by interacting with septin neck filaments and with Skt5p, which is a regulatory subunit of chitin synthase III (2). Bni4p is also involved in targeting protein phosphatase 1 (Glc7p) to the bud neck before bud emergence (2). Bni4p is required for the assembly of the chitin ring, and is also involved in septum formation and the maintenance of bud neck integrity (3).

Bni4p localization is regulated during the cell cycle, with the protein located on the exterior of the septin ring before budding and on the mother side of the collar after budding (4). Proper localization of Bni4p requires the actin cytoskeleton, and binding to Glc7p, since cells containing mutant bni4 that fails to associate with Glc7p display mislocalization of Bni4p (2, 4). Bni4 is phosphorylated in a cell cycle-dependent manner, and inactivation of the protein kinase Hsl1p affects Bni4p localization, but there is no evidence that Hsl1p directly phosphorylates Bni4p (2).

bni4 null mutants are viable, but display altered deposition of chitin, and mislocalization of Chs3p, Skt5p, and Glc7p (3, 2).

Last updated: 2005-09-20