Putnam Investments, the troubled US fund manager, is tightening control over PanAgora Asset Management, the quantitative fund management specialist, raising its stake from 50% to 80%.

Putnam is buying the additional 30% from Nippon Life Insurance Company, the financial details of the deal were not available. The three-way relationship dates from 1997 when Putnam became co-owner of PanAgora with Nippon Life, Putnam's strategic partner in Japan.