Class II genes of the XXXX major histocompatibility complex. Comparisons of the DQ and @entity27595 and beta genes.

@entity1 @entity1472 @entity3098 @entity535 @entity2036 @entity377 @entity27595
The @entity1 major histocompatibility complex, HLA, contains the genes of several class II molecules. We present here the molecular maps of the DQ and DX subregions and analyze the sequences of the polymorphic DQ alpha and @entity3098 genes as well as the @entity27595 and DX beta genes. The DQ alpha and @entity3098 genes are oriented in opposite directions, approximately 12 kilobases apart. The @entity27595 and DX beta genes are similarly oriented about 8 kilobases. The exon-intron organizations of the DQ alpha and @entity27595 genes are analogous to those of other class II alpha genes. Comparison of the DQ alpha gene sequence to three DQ alpha cDNA clones shows that @entity535 replacements are predominantly located between residues 45 and 80 in the @entity1472 -terminal domain. Analysis of the frequency of silent and replacement substitutions indicates that there is little selection against replacements in DQ alpha first domains. The exons encoding the second domains of DQ alpha and @entity27595 are virtually identical, suggesting that a gene conversion event has occurred between these genes. The DX beta gene is very similar to the @entity3098 gene but differs in the cytoplasmic portion. The DX beta gene contains a separate exon of 24 @entity2036 encoding the core of the cytoplasmic tail. This exon is not expressed in the @entity3098 genes due to a nonfunctional splice junction. Comparison of the number of @entity377 substitutions in the @entity3098 first and second domain exons suggests that little or no phenotypic selection acts on the first domain whereas the second domain is under strong selection.
