A new β₂ microglobulin mutation found in a melanoma tumor cell line

β₂ microglobulin mutations are an important mechanism for HLA class I total loss, (phenotype No. I) and have been described in colon carcinomas, melanomas and lymphomas. We describe a new β₂ microglobulin mutation detected in the melanoma cell line GR-34. The new mutation reported here was identified as a deletion of 4 bases (TTCT) in the highly repetitive sequence CTCTCTCTTTCT located in the leader sequence of the β₂ micmglobulin gene at codon 15-16 of exon 1. The mutation produces a frameshift in the open reading frame sequence with the appearance of a stop codon at position 42. We also demonstrate that the second β₂ microglobulin gene is deleted. Comparisons with β₂ microglobulin mutations in other tumor cell lines suggest a mutation hot spot in exon 1.