Sequence of a new class I null allele within the HLA-B44 specificity

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Acknowledgments: We thank the blood donor ALBA and her mother for their cooperation to this study. We also thank B. Kervaire and R. Zanone for expert technical assistance. This work was supported by the Swiss National Science Foundation (grant no. 32–52061.97 and no. 31–57557.99). A new HLA class I null allele has been identified within the B44 group by combined serological and molecular typing of a blood donor. Based on full‐length cDNA sequencing, this novel HLA‐B*4419N allele was found to differ from B*4402 by one single base pair deletion at position 7 of exon 1 which results in a stop at codon 19. This mutation was confirmed by polymerace chain reaction‐sequence‐specific oligonucleotide probe (PCR‐SSOP) hybridization on genomic DNA. Based on family typing, this new allele segregates with the haplotype A*01‐B*4419N‐Cw*0501‐DRB1*1301‐DRB3*0101. Since nonsense codons are generally associated with increased mRNA decay, we investigated B*4419N mRNA by semi‐quantitative reverse transcriptase (RT)‐PCR and by cDNA cloning efficiency. Comparison of B*4419N cDNA to B*4402 control cDNA and to B35 cDNA levels in the same donor, as well as the analysis of cloned inserts, revealed that the exon 1 mutation did not significantly influence B*4419N steady‐state mRNA.