 Shares of Nucor Corp. NUE, -3.97 sank 4.5 toward a seven-week low in premarket trading Wednesday, after the steel maker issued a third-quarter profit warning, as weakness in its steel mills business is offsetting strength in steel products. The company expects earnings per share of 6.30 to 6.40, down from 7.28 in the year-ago period, and below the FactSet EPS consensus of 7.56. 