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Brazil bourse previews Bovespa index changes, Itau tops Petrobras

BM&FBovespa SA, Brazil's sole financial bourse, offered a first look on Tuesday at its proposals for modifying the benchmark Bovespa stock index for the May through August period.

Shares of Brazil's largest nongovernment bank, Itau Unibanco Holding SA, would carry a 9.41 percent weighting on the index under the proposals, surpassing the preferred shares of state-run oil firm Petroleo Brasileiro SA, known as Petrobras, which would have a 7.29 percent weighting.

Petrobras has lost about half of its market value over the past three years, hurt by a government policy that forces the company to sell imported fuel at a loss to tamp down inflation.

A new Bovespa index weighting scheme this year takes into account market value as opposed to trading volume, which was used in previous years.

BM&FBovespa makes modifications to the index every four months.

Shares of mining company MMX Mineração e Metálicos SA were included in BM&FBovespa's preview, increasing the likelihood that they will be added to the official index for the period.

BM&FBovespa proposes removing from the index the shares of medical diagnostics firm Diagnósticos da América SA, known as Dasa SA, and logistics firm Prumo Logistica SA , formerly known as LLX.

(Reporting by Priscila Jordao; Writing by Asher Levine; Editing by Peter Galloway)