SAO PAULO (Reuters) -Brazilian retailers Americanas SA and Lojas Americanas SA took another step toward their planned merger here on Wednesday and said the stakes of their billionaire controlling shareholders will be diluted so that they hold 29.2% of the combined company, Americanas. Americanas SA was formerly known as B2W Digital. Brazilian billionaires Jorge Paulo Lemann, Marcel Telles and Carlos Alberto Sicupira, founders of 3G Capital, currently control Lojas Americanas here and will become "reference shareholders" and not hold more than 50% of the voting shares, the companies said in a securities filing. Shares rose sharply on the news. Preferred shares in holding Lojas Americanas were up 12.3% and common shares up 9% in late morning trading in Sao Paulo. Common shares of Americanas SA were up 5%. Although the company said controlling shareholders are not charging a premium, Americanas is proposing the adoption of a takeover defense mechanism. According to the company, any shareholder acquiring more than 15% of shares would trigger a tender offer to all shareholders. The mechanism known as a poison pill makes it more difficult for any investor to accumulate a stake similar to the reference shareholders. Itau BBA analysts said the deal was positive for Lojas Americanas, as it would enhance the company’s corporate governance structure and ease some investors’ concerns regarding corporate governance. Once the deal is concluded, shares issued by Americanas SA held by Lojas Americanas will be canceled and each shareholder of Lojas Americanas will receive 0.186 common share issued by Americanas, they added. The resulting combined company will be listed in the United States. The filing mentions the New York Stock Exchange and the Nasdaq and does not give a time frame for the listing. The filing also says the deal values Lojas Americanas SA net equity at 10.3 billion reais ($1.81 billion), while Americanas SA net equity is valued at 25.8 billion reais. Americanas SA has already received 6.3 billion reais in assets spun off from Lojas Americanas in a deal announced earlier this year, but both continued trading separately. ($1 = 5.6795 reais) Reporting by Gabriel Araujo and Tatiana Bautzer in Sao PauloEditing by Louise Heavens, Chizu Nomiyama and Matthew Lewis