MEXICO CITY (Reuters) - Mexican broadcaster Televisa has joined an investment firm owned by Bill Gates and four other private equity companies to explore a bid for U.S. Spanish language broadcaster Univision.

Univision (Research) said in a filing to the Securities and Exchange Commission on Friday that Televisa and Gates' Cascade Investment L.L.C were both in the group of companies studying their options for a bid.

Gates, the chairman of Microsoft Corp. (Research), manages private investments through Cascade Investment.

Bain Capital Partners LLC, Blackstone Management Associates V LLC, Carlyle Investment Management LLC, and Kohlberg Kravis Roberts & Co. L.P. are also part of the group, the filing said.

Televisa, the biggest producer of Spanish-language content in the world, declined to comment on Friday.

Univision Communications Inc. put itself up for sale in February.

Its main attraction to prospective buyers is its growth potential, as the Spanish-language advertising market in the United States has lagged the rapid growth of Hispanic audiences in the country.

Grupo Televisa (Research), which owns an 11.4 percent stake in Univision, had already authorized its top two executives to work on a plan to boost its investment in Univision.

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