Characterization of an HLA DR beta pseudogene.

Area of Science:

• Immunogenetics
• Molecular Biology
• Human Major Histocompatibility Complex (MHC)

Background:

• Class II molecules of the human MHC, including DR antigens, are crucial for immune responses.
• These molecules are composed of alpha and beta polypeptide chains.

Purpose of the Study:

• To isolate and characterize a specific human DR beta gene from genomic DNA.
• To identify mutations and understand the inactivation mechanism of the DR beta gene.

Main Methods:

• Isolation of DR beta gene using overlapping cosmid clones from genomic DNA.
• DNA sequencing to identify mutations and structural features.
• Analysis of nucleotide substitutions and predicted amino acid sequences.

Main Results:

• A DR beta gene was isolated, spanning over 20 kilobases with six exons.
• The gene contains multiple deleterious mutations, including splice junction deviations, premature termination codons, and a frameshift insertion, rendering it nonfunctional.
• Conserved amino acid residues were replaced, and nucleotide substitutions suggest post-inactivation changes.
• A Kpn I repeat insertion 5' to the promoter region may have inactivated the gene by disrupting transcription.

Conclusions:

• The isolated DR beta gene is a pseudogene due to significant inactivating mutations.
• The Kpn I repeat insertion is a potential cause of gene inactivation, affecting transcriptional regulation.
• This DR beta pseudogene appears to be present in other individuals with the DR4 haplotype.