UPDATE 1-E.ON signs Yuzhno Russkoye gas field deal

* Ruhrgas, Gazprom CEOs sign deal in Russia’s St. Petersburg

* E.ON to buy 25 pct of Yuzhno Russkoye from Gasprom

* Gazprom to take over from E.ON 49 pct in ZAO Gerosgaz

* E.ON Ruhrgas still to hold 3.5 pct of Gazprom via Gerosgaz

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FRANKFURT, June 5 (Reuters) - Germany's E.ON group EONGn.DE said on Friday it has signed a deal to complete the acquisition of a 25 percent stake in the Siberian Yuzhno Russkoye gas field from Gazprom OAO GAZP.MM, wrapping up more than four years of preparation to co-own the strategic asset.

Ruhrgas and Gazprom chief executives Bernhard Reutersberg and Alexei Miller signed the agreement in St Petersburg, the company said in a statement.

It entails Gazprom taking over from E.ON Ruhrgas its 49 percent interest in the Russian company ZAO Gerosgaz, which holds nearly three percent of Gazprom shares.

Via Gerosgaz, E.ON Ruhrgas is the owner of that share package, which will be transferred to Gazprom ownership.

E.ON Ruhrgas continues to hold 3.5 percent of Gazprom shares via Gerosgaz.

“We are...deepening our long-standing partnership with Gazprom based on mutual trust and are making an important contribution to security of supply for Germany and Europe,” said E.ON CEO Wulf Bernotat.

He reiterated E.ON’s long-term goal to source at least 10 billion cubic metres of gas from its own production.

E.ON Ruhrgas' relationship with Gazprom to source Russian gas goes back 35 years but it has been keen to become owner of parts of the huge Yuzhno Russkoye reserves, of which Gazprom sold a 35 percent minus one share stake to E.ON Ruhrgas peer Wintershall BASF.DE in 2006.

The gas field will partly supply gas to the Nord Stream pipeline under the Baltic Sea to Germany, which is envisaged to bring gas to Europe from late 2011.