Enzymatic method of construction of RNAi library

The present invention provides a process for preparing an enzymatically systematic RNAi library from the target DNA. In this method, target DNA is not only from cDNA or genomic sequences of a particular gene, may also be prepared from a cDNA library. The invention also provides a screening method capable of selecting clones with a iRNA expression construct having the desired silencing activity from RNAi library. In screening, which enables efficient selection by fusing and a target DNA reporter gene and negative selection marker.