Cloning and sequencing of the chicken egg-white avidin-encoding gene and its relationship with the avidin-related genes Avr1-Avr5.

The gene encoding chicken egg-white avidin (Avd) was amplified from chromosomal DNA, cloned and sequenced. The entire coding region of preavidin (pre-Avd) containing four exons was identified by comparing the Avd gene (1119 bp) with the cDNA. It has a high identity percentage (91-95%) with the previously isolated Avd-related genes 1-5 (Avr1-Avr5). Interestingly, comparison of Avd with the Avr genes showed that the introns were better conserved (on average 97%) than the exons (90%). The Avd gene, as well as the cDNA, encodes a Gln residue at position 53 of the mature protein, which is in contrast to the previously determined amino-acid sequence.