Herbert Smith is joining US firm Morgan Lewis & Bockius to advise Pearson on its deal with the Data Broadcasting Corporation (DBC).
The UK media group has merged its Financial Times (FT) asset management division with the Nasdaq-listed company in a bid to strengthen its online presence.
The reverse takeover will give Pearson a 60 per cent share valued at over £400m. It will also bring together the FT's site FT.com with CBS's Marketwatch.com.
DBC is represented by New York practice Camly Karlinsky & Stein. Philip Hoffman, Pearson's US president, says: "I have never worked with them before but it is [DBC's] normal counsel and they were actually quite good."
Herbert Smith, which is advising on English aspects of the deal, declines to comment.
German postal service Deutsche Post's £830m takeover of US freight group Air Express International (AEI) has been handled by US firms.