Targeted deletion of Mrad1. A, Top panel: Mrad1 genomic DNA; Bottom panel: targeting construct. White boxes: exons; Gray box: promotorless neo gene; black thin lines: introns; Black thick lines: DNA sequences outside of Mrad1 genomic DNA; Numbers above: lengths of introns in bp; Numbers below: lengths of exons in bp; White arrows: restriction enzyme cutting sites (targeting construct) and locations around the DNA sequence to be removed (genomic DNA); B, Southern blot analysis of the Mrad1 gene in mouse ES cells. Bands indicate wild-type and deleted Mrad1 allele. C, PCR to assess genotypes in mouse ES cells. Bands indicate wild-type and deleted Mrad1 allele. D, Southern blot analysis of the Mrad1 gene in mice. E, Mrad1 genotyping in mice using PCR.