Fig. 5. Transcripts in the HG21C insertion locus. (A) The structure of the tcf7 locus in wild type and the HG21C enhancer trap line. Blue boxes and a white box indicate exons and 5' UTR, respectively. Positions and directions of primers are shown. (B) Three 3' RACE products (thick lines) identified in homozygous embryos by using nested primers in the first exon. Broken lines indicate regions removed by splicing. (C) Two RT-PCR products (thick lines) identified in homozygous embryos using f3 and r3 primers. Broken lines indicate regions removed by splicing. Positions of premature stop codons are shown (TAA and TGA). (D) The 5' RACE products identified in homozygous embryos in heat-shocked and non heat-shocked conditions by using nested primers in the GFP gene. A broken line indicates an intron. Arrows indicate 5' ends of the 5' RACE products.