Structural organization of the avidin and biotin-binding protein genes. The coding region of each gene is composed of four exons and three introns (upper panel). The respective exon and intron sizes (in nt) are indicated. Sequences at the exon-intron junctions are presented in the lower part of the figure. AVR sequences are consensus sequences of different alleles/genes reported in this study. a/- is a variable site among AVR s meaning either a gap or adenine.