We describe an experimental procedure for the isolation of growth inhibitory sequences from a complex cDNA library. This approach first takes advantage of the SETGAP technique (selectable expression of transient growth arrest phenotype) to enrich for growth inhibitory sequences, followed by a screening procedure to identify individual cDNAs that inhibit cell proliferation. Here we provide a detailed description of the experimental protocol and report the characterization of two cDNA sequences isolated in our initial screen of a mouse cDNA library. One of these cDNAs encodes the mouse ubiquitin-conjugation enzyme UbcM2. The other encodes a truncated form of a novel WD40 repeat protein, named Bopl, which is conserved from yeast to human. Together, these results demonstrate a new approach for the isolation of growth suppressors from cDNA libraries, and identify a previously unknown gene likely to be involved in growth control.