Tokyo stocks opened lower Tuesday tracking overnight falls on Wall Street, with investors locking in gains following recent rises in Japanese markets. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 283.88 points, or 0.72 percent, from Monday to 39,048.86. The broader Topix index was down 24.84 points, or 0.91 percent, at 2,714.55. On the top-tier Prime Market, decliners were led by securities house, wholesale trade and insurance issues. At 9 a.m., the U.S. dollar fetched 148.13-15 yen compared with 148.15-25 yen in New York and 148.27-29 yen in Tokyo at 5 p.m. Mond…