Mutational analysis of β1-tubulin. (A) Sequencing of β1-tubulin cDNA from a control subject and a patient with thrombocytopenia (Q43P). A double base-pair substitution, AG to CC, was found at nucleotide positions 130 and 131 of the β1-tubulin gene, as could easily be detected in subcloned β1-tubulin reverse transcriptase (RT)-PCR fragments from this patient. (B) The region encompassing exon 2 (117-bp PCR product) was amplified from genomic DNA before allele genotyping using PvuII digestion (74 and 43 bp) and analysis by agarose gel electrophoresis. The CAG-to-CCC double substitution (Q43P) leads to a loss of PvuII digestion. (C) This mutation results in a replacement of the highly conserved Gln at position 43 for Pro.