MOSCOW, May 31 (Reuters) - The Russian rouble

weakened against the U.S. dollar on Friday, easing past the 90

threshold to a one-week low.

By 0715 GMT, the rouble was 0.56% lower at

90.35 to the dollar after trading in a range of 89.970 to

90.420.

Against the euro, the rouble fell 0.46% to

97.78 and dropped 0.49% to 12.43 against the yuan

.

Brent crude oil, a global benchmark for Russia's

main export, was flat at $81.82 a barrel.

Russian stock indexes fell. The dollar-denominated RTS index

fell 1.22% to 1,136.87. The rouble-based MOEX Russian

index lost 0.71% to 3,258.83.

($1 = 90.3525 roubles)