Mercilus was the 26th overall pick in this year's draft out of Illinois.
"It's great to get it off my mind and just concentrate straight on football and everything," he said. "Just more concentrating instead of having a monkey on my back, no doubt and just getting in front of the fans."
The 6-foot-4, 254-pound player was a defensive end in a 4-3 scheme at Illinois but has moved to outside linebacker in the 3-4 alignment the Texans use. He's happy with the progress he made in the practices leading up to this week's mini-camp, which wrapped up Thursday.
"I've grown up a lot, pretty fast, too," Mercilus said. "They shot it straight at us really fast, a hundred miles per hour and it's a lot of information to take in. But it was our time for these three days of the mini-camp to actually grow up and graduate and basically go out here and execute what they call."
He started just one season in college, but was the nation's leader in sacks with 16 and forced fumbles with eight. He earned Big Ten first-team honors and the Ted Hendricks Award as the top defensive end in the nation.
The Texans did not release financial terms of the deal.
Houston has two remaining unsigned draft picks in guard Brandon Brooks and receiver DeVier Posey, who were both chosen in the third round.
Also on Thursday, Houston signed free agents Keith Browner and Moran Norris, who spent the last three days at mini-camp trying out for the team. Browner, a defensive end and linebacker, played in 38 games in his last three seasons at California.
Norris, a 12-year veteran fullback, played for the Texans from 2002-05 before spending 2006 and 2007 with the 49ers. He spent the 2008 season with the Lions before returning to San Francisco for the last three years.
Mercilus wants to make mark with Texans
The Houston Texans are trying not to put too much pressure on first-round pick Whitney Mercilus as the rookie adjusts to the NFL.
But the outside linebacker may have made things harder on himself: He is wearing the jersey number of Houston's former star middle linebacker DeMeco Ryans, who was traded to Philadelphia this offseason.
He is aware of what Ryans did in that jersey and likes the high expectations that come with wearing it.
"The challenge is stepping up to expectations, especially fans throwing it out there," he said. (They say) `You know, you've got big shoes to fill.' I don't mind it at all. I'm just out here just trying to get better and make a name for myself."
Ryans was a second-round draft pick who was named the AP Defensive Rookie of the Year in 2006 before making two Pro Bowls and leaving Houston as the franchise leader in career tackles with 636 in his six-year career.
Unlike Ryans, who was thrown into a starting role almost immediately, Mercilus should have some time to learn and develop before he's expected to play a major role for the Texans.
"We look to continue to grow, and I think he just needs to contribute," fellow linebacker Brian Cushing said. "He doesn't need any added pressure of thinking he needs to be a certain player or have 10 sacks or anything like that. He just needs to play football like he can."
For now Mercilus is trying to make the transition from playing defensive end in a 4-3 scheme at Illinois to outside linebacker in the 3-4 alignment the Texans use. He started just one season in college, but was the nation's leader in sacks with 16 and forced fumbles with eight.
Houston was looking for an aggressive pass rusher to ease the loss of Mario Williams, who left as the team's career leader in sacks, when they chose him with the 26th pick in the draft.
"It's definitely an adjustment standing up because I've never done it, but it's basically the same thing as I've been doing as a defensive lineman," he said. "I have to read and pay attention to the personnel and formations and stuff like that."
He's feeling better about the change now that he has a few practices behind him. Wednesday was the second day of Houston's three-day mini-camp for rookies and other young players before the team takes a break before training camp.
"It's a lot better," he said of his work this week. "I'm playing a lot faster so I'm able to press a bit more and it just makes everything much easier for me to play and make plays."
The Texans love the size and athleticism of the 6-foot-4, 254-pound Mercilus and aren't worried about him picking up the new scheme.
"He has a lot of ability and should be able to help us a lot," coach Gary Kubiak said. "Mercilus, athletically, is probably even more than what we thought he was. He's excellent."
Mercilus, who finished with 57 tackles last season, joins a defense which made a remarkable turnaround last season to rank second in the NFL in yards allowed. The improvement helped Houston to a 10-6 record, the AFC South title and its first trip to the playoffs.
He's excited to be a part of a group that is looking to do even more in 2012.
"It's awesome because they have high expectations, so there are high expectations on my part also," he said. "I have to come in here and show them that making me their first pick was the best decision and contributing to what was great last year. This year is about building upon that and moving forward."