Human Molecular Genetics, Vol 6, 739-745, Copyright © 1997 by Oxford University Press
RJ Pomponio, TR Reynolds, H Mandel, O Admoni, PD Melone, GA Buck and B Wolf
Biotinidase recycles the vitamin biotin from biocytin upon the degradation
of the biotin-dependent carboxylases. We have identified a novel point
mutation within the biotinidase gene that encodes the signal peptide in two
unrelated individuals with profound biotinidase deficiency. Sequence
analysis of genomic DNA from these individuals revealed a G to A transition
(G100-->A) located 57 bases downstream of the authentic splice acceptor
site in exon B. Although this mutation predicts a G34S substitution, it
also generates a 3' splice acceptor site. Sequence of the PCR-amplified
cDNA from the homozygous child revealed that all the product was shorter
than that of normal individuals and was the result of aberrant splicing.
The aberrantly spliced transcript lacked 57 bases, including a second
in-frame ATG, that encode most of the putative signal peptide and results
in an in- frame deletion of 19 amino acids. The mutation results in failure
to secrete the aberrant protein into the blood. This is the first reported
example in which a point mutation creates a cryptic 3' splice acceptor site
motif that is used preferentially over the upstream authentic splice site.
The preferential usage of the downstream splice site is not consistent with
the 5'-3' scanning model, but is consistent with the exon definition model
of RNA splicing.
ARTICLES
Profound biotinidase deficiency caused by a point mutation that creates a downstream cryptic 3' splice acceptor site within an exon of the human biotinidase gene
Department of Human Genetics, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
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