ISSN:
1432-1432
Keywords:
MHC class II genes
;
Polymorphism
;
Gene conversion
;
Intron preservation
;
Artiodactyls
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Twenty-one different caprine and 13 ovine MHC-DRB exon 2 sequences were determined including part of the adjacent introns containing simple repetitive (gt)n(ga)m elements. The positions for highly polymorphic DRB amino acids vary slightly among ungulates and other mammals. From man and mouse to ungulates the basic (gt)n(ga)m structure is fixed in evolution for 7 × 107 years whereas ample variations exist in the tandem (gt)n and (ga)m dinucleotides and especially their “degenerated” derivatives. Phylogenetic trees for the α-helices and β-pleated sheets of the ungulate DRB sequences suggest different evolutionary histories. In hoofed animals as well as in humans DRB β-sheet encoding sequences and adjacent intronic repeats can be assembled into virtually identical groups suggesting coevolution of noncoding as well as coding DNA. In contrast a-helices and C-terminal parts of the first DRB domain evolve distinctly. In the absence of a defined mechanism causing specific, site-directed mutations, double-recombination or gene-conversion-like events would readily explain this fact. The role of the intronic simple (gt)n(ga)m repeat is discussed with respect to these genetic exchange mechanisms during evolution.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00175503
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