ProFootballTalk first reported news of the move.
The trade comes one day before Oakland begins offseason workouts. The Raiders reportedly were prepared to release Pryor if they didn't find a trade partner by the start of workouts, but the 49ers' interest prompted Seattle to part with a low draft pick rather than take a chance on waiting, per Rapoport. The team is comfortable with Matt McGloin as the backup behind new starter Matt Schaub, who was acquired last month in a trade with the Houston Texans.
General manager Reggie McKenzie told reporters at the NFL Annual Meeting last month that Pryor asked to be let go. "Terrelle wants to start so bad," McKenzie said. "I'll visit with him. We'll talk to him."
Citing Raiders sources, however, Rapoport reported on Monday that "The Tebow Effect" was one reason for the team letting Pryor go. He was popular with fans but not on the field much, thus becoming divisive through no fault of his own.