O'Brien leaves Penn State less than two years after replacing Joe Paterno. He returns to the NFL to coach the team with the league's worst record this season.
The Texans made it official Thursday. Penn State picked defensive line coach Larry Johnson as interim head coach while the search for a replacement goes on.
A former offensive coordinator for the New England Patriots, O'Brien took on perhaps college football's toughest job in January 2012, joining a school rattled by the Jerry Sandusky child sex abuse scandal.
Despite a lack of scholarships, a bowl ban, an overall sense of doom and player defections from the late Paterno's roster, O'Brien led the Nittany Lions to two winning seasons while restoring some tempered enthusiasm in Happy Valley.
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