The present invention provides a system and methods for analyzing the function of nucleotide integrases and modified group II introns. The system comprises a donor plasmid comprising a wild-type or modified group II intron, a recipient plasmid comprising a DNA recognition site and a promoterless reporter gene downstream of the DNA target site, and a host cell. The method comprises the steps of transforming a host cell with the donor and recipient plasmids, assaying for expression of the reporter gene, isolating plasmid DNA from the cotransformed cells, and analyzing the plasmid DNA to confirm that the group II intron has been inserted into the target sequence. The present invention also provides a method for simultaneously analyzing the activity of two or more modified nucleotide integrases. The present invention also relates to methods of preparing a library of donor plasmids containing a plurality of diverse modified group II intron DNA sequences.