5' regulatory nucleotide sequence of an HLA-A*0101null allele.

We have previously demonstrated an HLA-A0101null allele segregating in a family with the HLA-B8, -Cw7, -DR3, -DR52, -DQ2 haplotype. In the present study the regulatory elements with known transcription enhancement activity of the silenced HLA-A0101 allele were analyzed. In the enhancer B element, a T was substituted for a C at position - 106, whereas no other alterations were found in the adjacent 5' section of the HLA-A0101null allele. This substitution was not seen in the enhancer B elements of the corresponding genes involved in normal HLA-A0101 membrane expression. Comparison of enhancer B element sequences of classical functional major histocompatibility complex (MHC) class I alleles demonstrated a high degree of conservation. In contrast, many MHC class I pseudogenes showed mutation in their enhancer B boxes. These results may indicate that the single mutation detected in the enhancer B element plays a pivotal role in the abolishment of membrane expression of the HLA-A*0101null allele.