Total U.S. money market mutual fund assets fell $2.54 billion to $2.575 trillion for the week that ended Wednesday, according to the Investment Company Institute.Assets of the nation's retail money market mutual funds rose $2.12 billion to $890.22 billion, the Washington-based mutual fund trade group said Thursday. Assets of taxable money market funds in the retail category rose $2.07 billion to $701.58 billion. Tax-exempt retail fund assets rose $50 million to $188.64 billion.Meanwhile, assets of institutional money market funds fell $4.66 billion to $1.685 trillion. Among institutional funds, taxable money market fund assets fell $4.62 billion to $1.605 trillion. Assets of tax-exempt funds fell $30 million to $80.32 billion.The seven-day average yield on money market mutual funds fell to 0.02 percent from 0.03 percent in the previous week that ended Tuesday, according to Money Fund Report, a service of iMoneyNet Inc. in Westborough, Mass.The 30-day average yield fell to 0.02 percent from 0.03 percent last week. The seven-day compounded fell to 0.02 percent from 0.03 percent. The 30-day compounded yield also fell to 0.02 percent from 0.03 percent, Money Fund Report said.The average maturity of portfolios held by money market mutual funds was unchanged at 49 days.The online service Bankrate.com said its survey of 100 leading commercial banks, savings and loan associations and savings banks in the nation's 10 largest markets showed the annual percentage yield available on money market accounts was unchanged from the week before at 0.11 percent.The North Palm Beach, Fla.-based unit of Bankrate Inc. said the annual percentage yield available on interest-bearing checking accounts was flat from the week before at 0.05 percent.Bankrate.com said the annual percentage yield on six-month certificates of deposit rose to 0.19 percent from 0.18 percent. It rose to 0.30 percent from 0.29 percent on one-year CDs. It was flat at 0.45 percent on two-year CDs. It fell to 0.44 percent from 0.45 percent on two-and-a-half-year CDs. It fell to 0.93 percent from 0.94 percent on five-year CDs.