An eGFP-expression construct was inserted behind the ATG start codon in the first exon. A loxP-flanked neomycin selection cassette was inserted into intron 1. The neomycin cassette was removed via Cre-mediated recombination. This allele expresses a eGFP-Tref1 fusion protein with colocalizes with endogenous gene product at telomeres. (J:225055)