Complementary DNAs encoding precursor molecules of the pituitary glycoprotein hormone (PGH) alpha- and luteinizing hormone (LH) beta-subunits of Japanese quail were isolated from a quail adenohypophyseal cDNA library using corresponding chicken cDNAs as hybridization probes. The isolated cDNAs had a length of 695 and 724 bp, respectively, and contained sequences of 5' and 3' untranslated regions and an entire coding region of the precursor molecules. Two series of incompletely repeating and partially overlapping nucleotide sequences were observed over a part near the 3' end of the apoprotein coding region and the 3'-untranslated region in the beta-subunit cDNA. One of them consisted of two repeated sets of 71 bases and the other consisted of six repeated sets of 30 bases or less. The predicted amino acid sequence showed that signal peptide and apoprotein of the alpha-subunit consisted of 24 and 96 amino acid residues, respectively, and those of the beta-subunit consisted of 47 and 119 amino acid residues, respectively. Hybridization of the quail PGH alpha- and LH beta-subunit cDNAs to adenohypophyseal RNA showed that sizes of PGH alpha- and LH beta-subunit precursor mRNAs were about 1.1 and 0.9 kb, respectively. Amounts of both mRNAs were increased three to four times by castration in male quail. A comparison of the amino acid sequences of each of the PGH alpha- and LH beta-subunit precursors of the quail and other vertebrates indicated that the apoprotein, especially that of the alpha-subunit, was conserved (59 to 85% and 34 to 55% homology in the alpha- and beta-subunits, respectively), while the signal peptide was diversified (4 to 75% and 4 to 45% homology in the alpha- and beta-subunits, respectively). In the LH beta-subunit apoprotein, interclass homology values varied in a narrow range and did not show a clear relation with the phylogenic distance, while interclass homology values in the alpha-subunit apoprotein and both signal peptides reflected the phylogenic distance. This characteristic feature of the LH beta apoprotein can be explained by assuming that the variable portion of the LH beta apoprotein molecule evolved with a higher speed than that of the other peptides, and consequently no sequence common with other classes remained. This highly variable sequence may be responsible for the high animal-class specificity of the interaction between LH and its receptor.