The investment seeks investment results that correspond generally to the price and yield performance, before fees and expenses, of The BofA Merrill Lynch Constrained Duration US Mortgage Backed Securities IndexSM. The underlying index reflects the performance of a selection of investment-grade U.S. agency residential mortgage-backed pass-through securities. The fund may also invest up to 20% of its assets in cash and cash equivalents, including shares of money market funds advised by NTI or its affiliates, futures contracts, options on futures contracts, options and interest rate and total rate of return swaps.