UPDATE: 5/13/14, 3:15 p.m. EDT. Additional information on the legal team for MPS and Silver Lake has been added to the eighth and ninth paragraphs of this story.

Payment-processing services provider Vantiv has turned to Wachtell, Lipton, Rosen & Katz for counsel on its acquisition of Mercury Payment Systems from private equity firm Silver Lake Partners.

Wachtell corporate partners Steven Rosenblum and Matthew Guest are advising suburban Cincinnati-based Vantiv on the $1.65 billion deal, which was announced late Monday.

Other lawyers from the firm working on the matter include executive compensation and benefits partner Jeannemarie O’Brien, restructuring and finance partner Gregory Pessin, tax partner Joshua Holmes and associates Erica Bonnett, Franco Castelli, Lauren Cooper Bilzin, Brandon Price, Francisco Morales, Jesse Payne-Johnson and Michael Sabbah. Nelson Greene serves as general counsel for Vantiv, which has paid Venable $80,000 since last year to lobby on payment processing and financial services industry issues, according to U.S. Senate filings.

Vantiv—which expects its acquisition of MPS to close in the second quarter—was once a joint venture between private equity firm Advent International and Cincinnati-based Fifth Third Bancorp before raising $575 million through an initial public offering in 2012. The listing generated $6 million in legal fees and expenses for Weil, Gotshal & Manges, Davis Polk & Wardwell and Sullivan & Cromwell, according to our previous reports.

MPS itself sought to go public earlier this year, filing confidentially in December under the JOBS Act before announcing in March its intention to raise at least $100 million via an IPO. Simpson Thacher & Bartlett capital markets partners William Hinman Jr. and Daniel Webb—both of whom took lead outside counsel roles for the underwriters on Facebook’s $16 billion IPO in 2012—have been representing MPS in its effort to go public, with Ropes & Gray advising underwriters led by Barclays, JPMorgan Chase and Morgan Stanley.

An SEC filing made in connection with the scuttled IPO—The New York Times’ DealBook reports that Silver Lake started a quick sales process after suitors expressed interest in buying MPS—shows that Ropes and some of its attorneys are limited partners of “RGIP LP, which is an investor in certain investment funds affiliated with Silver Lake.”

RGIP owns equity interests representing less than 1 percent “of the aggregate of the outstanding shares and units of each of our Class A common stock and Class B common stock and the holdings units” of MPS, according to an S-1 filing by the company. The filing also states that an investment vehicle “comprised of certain” Simpson partners, members of their families and related individuals “owns interests representing less than 1 [percent] of the capital commitments of certain investment funds affiliated with Silver Lake.”

Silver Lake, a longtime Simpson client, has tapped the firm to handle its side of the MPS sale. William Dougherty, a private equity and M&A expert who took Simpson’s leadership reins last year, is leading a team from the firm that includes employee benefits partner Tristan Brown and associates Ravi Agarwal, Thomas Asmar and Austen Heim. Andrew Liazos, head of the executive compensation practice at McDermott Will & Emery in Boston, is also working on the matter.

MPS chief legal officer Ross Agre and associate general counsel Ryan Stahl are heading up the in-house side for Durango, Colo.–based MPS, along with Silver Lake managing director and general counsel Andrew Schader. Simpson alum Karen King serves as Menlo Park, Calif.–based Silver Lake’s managing director and chief legal officer. (Silver Lake was one of several Simpson clients that figured in criminal and civil insider trading complaints filed last month against former firm managing clerk Steven Metro.)

Silver Lake tapped Simpson for counsel in December on William Morris Endeavor Entertainment’s $2.4 billion acquisition of entertainment industry rival IMG Worldwide. The firm had previously advised the buyout shop on its purchase of a 31 percent stake in WME in 2012.

Simpson’s role representing Silver Lake on its sale of MPS wasn’t the firm’s only big transactional move Monday. Simpson, which debuted a new website this week, also took the lead advising Pinnacle Foods on its $6.6 billion sale to Hillshire Brands.