Tukuafu had spent his career with San Francisco before being placed on injured reserve at the end of training camp and later released. He played in only two regular-season games last year with the 49ers, but was part of all three playoff games for San Francisco. Tukuafu appeared in 14 of 16 regular-season games with San Francisco in 2012.
Tukuafu said he had been working out at the University of Oregon since being cut.
Fort was on Seattle's practice squad but was signed to the active roster in case Malcolm Smith (groin) is unable to play Sunday.