Morrison & Foerster and Skadden, Arps, Slate, Meagher & Flom have the lead roles advising Japanese Internet and telecommunications group SoftBank Corp. on its proposed $20.1 billion purchase of ailing American mobile carrier Sprint Nextel Corp.

SoftBank will distribute $12.1 billion to existing Sprint shareholders and inject another $8 billion to strengthen Sprint’s balance sheet. The deal will give the Japanese company a 70 percent share in a new publicly traded company called New Sprint. The transaction, which is subject to shareholder and regulatory approval, is expected to close in mid-2013.