A small 6 nt inversion and substitution of two T nucleotides with a single A resulted in a frameshift and introduction of a stop codon 5 amino acids downstream in the encoded protein. This mutation is predicted to lie in the head domain of the protein. Northern blot analysis indicated that mRNA expression, size, and stability were unaffected. Immunoblot analysis showed that less than 1% of the normal level of the protein was expressed.