Jackson, a seven-year pro who spent his entire career with the Seahawks, gradually fell out of favor with Seattle general manager Tim Ruskell in recent months amid injuries and attitude concerns.

But with few tempting offers for Jackson, the Seahawks improbably helped the 49ers _ who beat NFC West champion Seattle twice last season _ at San Francisco's leanest position.

"You know that makes it that much sweeter that I can go back and face my old team," said Jackson, who's signed through 2009. "I've been looking forward to becoming a 49er ever since I heard the talk about the trade."

San Francisco gave up the 124th overall pick, and the Seahawks used it on Georgia Tech offensive lineman Mansfield Wrotto.

Jackson's tenure in Seattle included three 1,000-yard seasons and 47 touchdowns, but also several minor skirmishes with team brass ever since a contract dispute several years ago. He had a truculent attitude toward offseason workouts, and Jackson also missed 13 games over the last two seasons with injuries.

"Ever since I have been here, we all know he has not been happy," said Ruskell, who joined the Seahawks in 2005. "We want you to want to be here. We want you to be happy to be a Seahawk and work well with your teammates. That's what we want, and we just never really seemed to get to that point.

"Yeah, he is a good player, we all know that, and it wasn't about the catches and the yards, but it just never felt comfortable as a fit."

Jackson caught 63 passes for 963 yards and a career-high 10 touchdowns last season. He was leading the NFL in touchdown receptions late last season before he missed three games with turf toe.

Seattle, which signed Nate Burleson before last season, acquired Deion Branch from New England in September, then signed the former Super Bowl MVP to a $39 million contract.

Ruskell said the 49ers' interest in Jackson didn't intensify until just before the draft. Jackson passed a physical in Santa Clara and visited with 49ers coach Mike Nolan on Saturday, and the Seahawks agreed to the trade Sunday morning.

Jackson could tell Ruskell had soured on him months ago, particularly on issues around his contract.

"I was promised certain things and I was slated on certain things, and when the new regime came in, they didn't really want to hear that," Jackson said. "Tim Ruskell is just going in a new direction. He brought in a good player in Deion Branch. He brought in a good player in Nate Burleson. I guess he really liked those guys, and I wasn't one of his guys."

Jackson joins free-agent signee Ashley Lelie, veterans Arnaz Battle and Bryan Gilmore and third-round pick Jason Hill in the 49ers' receiving corps. Jackson said he intends to participate in the 49ers' minicamp next weekend to get a quick start on the open competition for both starting spots.

"He gives us a receiver that's proven in the NFL," Nolan said. "He's very productive. He's in the division, and that's important. He's going to compete with Arnaz, and we'll see how that goes. That will be interesting."

The 49ers were desperate for a top-flight receiver after cutting Antonio Bryant earlier in the offseason, and several 49ers have prior experience with Jackson. Backup quarterback Trent Dilfer threw passes to Jackson while both were in Seattle, and personnel chief Scot McCloughan previously was a Seahawks executive.