The yield on a closely watched index of 30-year triple-A rated, tax-exempt municipal securities climbed 0.12 percentage point higher to close at 4.48% Tuesday, according to Municipal Market Data.

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Fannie and Freddie's debt and securities are exempt from regulations that limit banks' exposure to the securities of any single private company.

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But the municipal securities market is thinly traded and largely exempt from the controls of both the Securities Act of 1933 and the Securities Exchange Act of 1934.

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