The gene trap vector inserted into intron 3 of the gene. The insertion of the trap sequence introduces a splice acceptor, a stop codon and a strong polyadenylation site, thus splicing nascent transcripts of the Ccnt1 gene to the trap to create a fusion protein between CCNT1 and beta-geo, which contains only 18% of CCNT1 amino acid sequence. Western blot analysis of cell lysates from various organs demonstrated that, when normalized to levels of total protein, homozygous mutant mice exhibit some residual (less than 5%) expression of CCNT1 protein relative to wild-type controls. (J:130071)