Identification of the new allele B*3556 and extension of the sequences of B*4420 and B*4427.

A new B*35 allele, B*3556, was identified in a Caucasian individual. Direct sequencing of exons 2 and 3 revealed that B*3556 was identical to B*3503, except for a nucleotide substitution from G to A at position 302, which causes a change from AGC to AAC at codon 101. This results in an amino acid change from Ser to Asn at position 77 of the mature protein. Two B*44 alleles, B*4420 and B*4427, were detected in a liver recipient and in an unrelated bone marrow donor, respectively, and their sequences were confirmed. The sequences of exons 1,4 and 5 were also elucidated; for B*4420, these exons proved to be identical to those of B*440201. The sequence of exon 5 of B*4427 showed three mismatches with that of B*440201, implicating that it probably arose from B*440201 by allele conversion with an allele of the B*15, 45, 46, 49 or 50 allele group. Elucidation of the sequence of introns 3 and 4 indicated that the breakpoint for allele conversion has to be located in intron 3 or exon 4.