Bain Capital and TPG Capital have official become the lead investors in Quintiles Transnational.

The international contract research organization said the deal closed on Thursday in which Bain Capital and TPG Capital bought out the ownership share of One Equity Partners in Quintiles. The amount has not been disclosed, but media reports have said it was in excess of $3 billion.

Dennis Gillings, the founder, chairman and chief executive officer of Quintiles, remains an investor and head of the company.

Other investors in Quintiles include 3i and Temasek Holdings.

The change in investors was reported in December.

One Equity is the private equity arm of Wall Street giant JPMorgan. It provided the bulk of the financing in 2003 when Gillings put together a $1.7 billion deal to take Quintiles private.

Quintiles is in the midst of a major expansion plan that includes a new headquarters building and the addition of some 1,000 jobs in the Triangle.

Gillings launched the company in 1982 while working as a professor at the University of North Carolina at Chapel Hill.

"Our new investor partnership is a strong reinforcement of Quintiles’ brand and growth strategy," Gillings said in a statement issued in December, "and has been spurred by our record performance. We are pleased to move forward with our financial partners Bain Capital, TPG, 3i and Temasek. The strength of our capital structure and partnership with these leading global investors underscore our unsurpassed ability to bring innovative solutions to the pharmaceutical and biotech industries. I also want to thank One Equity Partners for their contributions over the past four years."