Nervous investors bought ultra-safe U.S. government bonds, pulling the yield on the 10-year Treasury note down to 2.32 percent from 2.39 percent late Friday. Weekend negotiations on Greece's bailout terms produced no breakthroughs and Greek officials and creditors remained far apart as a deadline for a debt payment nears. Greek leaders want to get access to the final 7.2 billion euros ($8.2 billion) of their bailout program that's needed to repay debts and avoid a possible default that could trigger an exit from the euro; the bailout package expires at the end of the month. THE QUOTE: "We have always argued that a Greek deal would only occur at one minute to midnight," Michael Every, Rabobank's head of Asia-Pacific financial market research, wrote in a commentary. The country's securities regulator issued draft rules Friday limiting the amount investors can borrow from brokerages for trading to four times their net capital, according to a report by the official Xinhua news agency. Authorities are clamping down as they try to prevent a crash in China's overheated stock markets, which have soared in the past year in a boom fueled partly by borrowed money. Benchmark U.S.