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This allele encodes a high affinity, heat labile, 104 kDa receptor containing 848 amino acids. Sequencing studies of cDNA from C57BL/6J congenic mice homozygous for this allele identified nucleotide substitutions in the ORF that would cause 5 amino acid differences between the C57BL/6J and BALB/cBy peptides, and 2 amino acid differences between the BALB/cBy and DBA/2J peptides. A T to C transition in exon 11 replaces the opal termination codon in the C57BL/6J allele with an arginine codon in the BALB/cBy allele. This change would extend translation of the BALB/cBy mRNA by 43 amino acids, accounting for the larger size of the peptide produced by this allele (104 kDa, vs 95 kDa for the C57BL/6J allele).

C57BL/6 carries the responsive Ahr^b allele; DBA/2 carries nonresponsive Ahr^d. Heterozygotes (Ahr^b/Ahr^d) are responsive (J:5282). Later work identified a second (J:8895) and later a third (J:22144) allele conferring response. Thus the allele in C57, C58, and MA/My strains is now Ahr^b-1; Ahr^b-2 is carried by BALB/cBy, A, and C3H; and Ahr^b-3 by Mus spretus, M. caroli, and MOLF/Ei. The nonresponsive strains AKR, DBA/2, and 129 carry Ahrd (J:22144). Nucleotide and amino acid sequence differences between Ahr^b-1 and Ahr^d have been determined (J:17460).

Strain of origin - this allele was found in BALB/cByJ, A/J, C3H/HeJ, CBA strains

Sequencing of the gene revealed a 5293 nucleotide insertion in the 3' noncoding region. The inserted sequence is a variant of the intracisternal A-particle elements. Mice carrying this allele express a reduced amount of the major gene transcript. The encoded mRNA contains a normal coding region and an abnormally long untranslated region.

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