After the 177-point fall on Thursday, the sell-off continued on Dalal Street on Friday. A steep fall in select cement and banking shares pulled down the Bombay Stock Exchange Sensex further sharply by 150.30 points to end at 12,285.11 on persistent heavy selling by funds and operators.The Sensex opened low at 12,400.71 as against 12,435.41 yesterday and soon plunged to 12,224.44. Thereafter, it recovered marginally and closed at 12,285.11, still showing a sharp fall of 1.21 per cent over previous close. Similarly, the National Stock Exchange S&P CNX Nifty fell sharply by 51 points or 1.38 per cent to 3650.05 from 3701.05 yesterday.Cement giants like ACC, GACL and Grasim declined sharply on heavy pressure after reports that the government today threatened to ban cement exports or impose a cess if cement companies failed to initiate voluntary steps by May 15 to check spiralling prices of the commodity.