Molecular cause of the negative RHD promoter PCR in Cdes. The nucleotide sequence of the Cdes, RHD and RHCE promoter reaching from about 1550 to 901 bp 5' of the A of the start codon is shown. The positions of the RHD specific primers re011d and re012 used for the RHD promoter PCR are given. Nucleotides indicating RHD or RHCE origin of the Cdes sequence are highlighted. The Cdes promoter sequence represents RHD. A small DNA stretch of at least 13 bp in the region of re012 is replaced by the corresponding sequence of RHCE. This gene conversion caused the negative result obtained in the RHD promoter PCR-SSP (Fig. 2). RHCE nucleotide sequence is according to GenBank accession number AL031284.