Fig. 3. In vivo TCR events during maturation of T-cell clones F1 and MFS6 M2. During T-cell maturation, V(D)J-mediated rearrangements occur at the TCRα locus, generating V-J coding joints and cleaved signal ends. Both mutant clones underwent a rearrangement that resulted in the formation of a non-functional V-J coding joint V23 joined to J48 (F1) or V35 joined to J46 (MFS6 M2) (colored boxes), and their respective cleaved signal ends. A subsequent rearrangement occurred in an attempt to form a functional TCRα, generating cleaved signal ends that included the observed non-functional V-J coding joint. These TCRα signal ends were inserted via a transposition reaction into intron 1 of the HPRT gene. The non-functional V-J coding joints were observed in the cDNA due to correct splicing as an exon into the mRNA.