The BSE benchmark Sensex was trading 55 points down in late morning trade on profit-booking by funds and retail investors.The 30-share barometer which had declined 33 points in early trade , moved 55 points down to 16,808 a short while ago.In a similar fashion, the wide-based National Stock Exchange index Nifty shed 10.05 points to 5,105.85 when reports last came in.