Donor construct for ends-out homologous recombination, which is designed to knockout the mir-let7, mir-125 and mir-100 microRNAs. The construct contains a 4.1kb fragment from the region containing these microRNAs as the left arm of the targeting vector. This fragment is fused to a Scer\GAL4 coding region. The construct also contains a 2.7kb fragment from the region containing these microRNAs as the right arm of the targeting vector. The vector also contains a w+* marker and an RS(I-SceI) site.