Reticulocyte mRNA analysis. (A) 5′RACE on reticulocyte mRNA, using the pairs of primers I/IX (left side) and I/X (right side). C, control; I.2, proposita. The PCR products are schematically represented and their sizes in basepairs are shown. For schematic representation of exons, see Fig 1. (B) Use of internal cryptic splicing sites within exon 13. Sequencing analysis performed on RT-PCR products derived from normal12 or 4.1 Annecy (this report) mRNAs showed discrete use of cryptic acceptor sites within exon 13. The several sequences obtained from 4.1 Annecy tend to suggest a different pattern of use of these sites. () Major site; (—) secondary site; (---) site not used. Intronic and exonic sequences are represented in lowercase and capital bolded letters, respectively.