Divergent evolution of part of the involucrin gene in the hominoids: unique intragenic duplications in the gorilla and human.

The gene for involucrin, an epidermal protein, has been remodeled in the higher primates. Most of the coding region of the human gene consists of a modern segment of repeats derived from a 10-codon sequence present in the ancestral segment of the gene. The modern segment can be divided into early, middle, and late regions. We report here the nucleotide sequence of three alleles of the gorilla involucrin gene. Each possesses a modern segment homologous to that of the human and consisting of 10-codon repeats. The early and middle regions are similar to the corresponding regions of the human allele and are nearly identical among the different gorilla alleles. The late region consists of recent duplications whose pattern is unique in each of the gorilla alleles and in the human allele. The early region is located in what is now the 3' third of the modern segment, and the late, polymorphic region is located in what is now the 5' third. Therefore, as the modern segment expanded during evolution, its 3' end became stabilized, and continuing duplications became confined to its 5' end. The expansion of the involucrin coding region, which began long before the separation of the gorilla and human, has continued in both species after their separation.