There are three types of mouse Mutyh mRNAs (type a, b and c) generated by alternative splicing, and type b mRNA is a major form among the three in most of the tissues examined. The level of type c mRNA is relatively high in brain. Type a and b mRNAs were expected to encode 57.7 kDa protein (MUTYHα), while type c mRNA had a partly different open reading frame encoding a 50.2 kDa protein (MUTYHβ). An in vitro translation of type b and c mRNAs produced a 50 kDa MUTYHα and 47 kDa MUTYHβ, respectively. MUTYHα and MUTYHβ were detected in wild-type embryonic stem (ES) cells or thymocytes prepared from wild-type mice, but neither MUTYH-null ES cells nor thymocytes prepared from MUTYH-null mice. Both MUTYHα and MUTYHβ were mainly localized in the nuclei and some in mitochondria in wild-type ES cells. Recombinant MUTYHα and β were expressed as fusion proteins with thioredoxin in Escherichia coli, but only MUTYHα was partly soluble and thus could be purified. Recombinant MUTYHα possessed DNA glycosylase activities to excise adenine opposite 8-oxoguanine and guanine but not AP lyase activity.
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