MM B cells express aberrant splice variants of HAS1. A schematic representation of HAS1Va (A), HAS1Vb (B), and HAS1Vc (C). ▦ represents exons, while ▪ indicates retained fragments of intron 4. Introns are shown with solid lines. Original stop codons of each novel variant are marked with italic letters, while bold uppercase letters indicate start codons and PTC. (A) HAS1Va: Point mutation 7760C>T detected in this novel variant transcript is shown in bold, uppercase letters; PTC is located 56 nucleotides downstream of deleted exon 4. (B) HAS1Vb is the result of deletion of the entire exon 4 and partial retention of intron 4 (59 bp; 12 first and last nucleotides of retained introns are shown) at the 5′ end of exon 5. These aberrations harbored PTC 93 nucleotides downstream of the retained intron 4. (C) HAS1Vc intronic splice variant is similar to HAS1Vb and is the result of the retention of 26 nucleotides of intron 4, causing insertion of a PTC, TAA, at the 3′ end of exon 4. The 26 nucleotides of retained intron 4 are shown on the figure. PTC is shown in bold uppercase letters.