Gene conversion of two functional goat alpha-globin genes preserves only minimal flanking sequences

We have determined the complete nucleotide sequence of the nonallelic adult goat I alpha- and II alpha-globin genes and, as is the case with the duplicated human alpha-to each other. Such high homology (99%) has most likely been preserved via a gene conversion mechanism. The conversion unit in goats is only about 9000 base pairs in length, and contained within this short region are all the known signals required for accurate and efficient transcription, with the CCAAT box adjacent to the 5'-boundary of the conversion unit and the poly(A) addition site adjacent to the 3' end. This conversion unit is also flanked by a 23-base-pair direct repeat "boundary sequence," vestiges of which are also observable in the human and mouse alpha-globin genes and pseudogenes. These direct repeats imply that a transposition-like event may have been responsible for the insertion of an ancestral alpha-like sequence into a new chromosomal locus, and that this insertion event and subsequent gene duplication may have predated the mammalian radiation.