Ancient and recent intron stability in the Artemia hemoglobin gene

Artemia has evolved three distinct hemoglobins formed by the association of two nine-domain globin polymers. Sequence analysis of cDNA clones corresponding to two polymers, named T and C, indicates that their genes are the products of a duplication event some 60 million years ago. The present study indicates the presence of 22 introns in each of the T and C polymer genes. The 22 introns are classified into two groups: 17 correspond to positions within globin domains, and 5 correspond to interdomain linkers (or N- and C-terminal extensions). Intron position and reading frame phase are precisely conserved between T and C polymers for all 22 introns, but within each gene the position and phase are not always consistent from domain to domain or from linker to linker. The discordance of Artemia hemoglobin introns is discussed in terms of different model mechanisms and constraints: intron sliding, intron loss or gain, and the exon definition model of primary transcript RNA splicing. The results suggest that constraints of pre-mRNA processing should be considered when considering intron positional changes in homologous genes.