Blood, Vol. 92 No. 5 (September 1), 1998:
pp. 1776-1784
Rh50 Glycoprotein Gene and Rhnull Disease: A Silent
Splice Donor Is trans to a Gly279
Glu
Missense Mutation in the Conserved Transmembrane Segment
Cheng-Han Huang,
Zhi Liu,
Guangjie Cheng, and
Ying Chen
From the Laboratory of Biochemistry and Molecular Genetics, Lindsley
F. Kimball Research Institute, New York Blood Center, New York, NY.
Rhnull disease includes the amorph and regulator types
that are thought to result from homozygous mutations at the
RH30 and RH50 loci, respectively. Here we report an
unusual regulator Rhnull where two G
A nucleotide
(nt) transitions occurred in trans, targeting different
regions of the two copies of Rh50 gene. The nt 836 GA mutation was a missense change located in exon 6; it converted Gly into
Glu at position 279, a central amino acid of the transmembrane segment
9 (TM9). While cDNA analysis showed expression of the 836A(Glu279) allele only, genomic studies showed the
presence of both 836A(Glu279) and 836G(Gly279)
alleles. A detailed analysis of gene organization led to the
identification in the Rh50(836G) allele of a defective donor splice
site, caused by a GA mutation in the invariant GT element of
intron 1. This is the first known example of such mutations that has
apparently abolished the functional splicing of a pre-mRNA encoding a
multipass integral membrane protein. With a silent phenotypic copy in
trans, the negatively charged Glu279 residue may
disrupt TM9 and impair the interaction of the missense protein with
Rh30 polypeptides. To evaluate the significance of the mutation, we
took a comparative genomic approach and identified Rh50 homologues in
different species. We found that Gly279 is a conserved
residue and its adjacent amino acid sequence is identical from
Caenorhabditis elegans to human. These findings
provide new insight into the diversity of Rhnull disease and suggest that the C-terminal region of Rh50 may also participate in
protein-protein interactions involving Rh complex formation.
© 1998 by The American Society of Hematology.
