Molecular cloning of a cDNA encoding mouse DNA helicase B, which has homology to Escherichia coli RecD protein, and identification of a mutation in the DNA helicase B from tsFT848 temperature-sensitive DNA replication mutantcells

DNA helicase B is a major DNA helicase in mouse FM3A cells. A temperature-s ensitive mutant detective in DNA replication, tsFT848, isolated from FM3A c ells, has a heat-labile DNA helicase B. In this study, we purified DNA heli case B from mouse FM3A cells and determined partial amino acid sequences of the purified protein. By using a DNA probe synthesized according to one of the partial amino acid sequences, a cDNA was isolated, which encoded a 121 .5 kDa protein containing seven conserved motifs for DNA/RNA helicase super family members. A database search revealed similarity between DNA helicase B and the a subunit of exodeoxyribonuclease V of a number of prokaryotes in cluding Escherichia coli RecD protein, but no homologous protein was found in yeast. The cDNA encoding DNA helicase B from tsFT848 was sequenced and a mutation was found between DNA/RNA helicase motifs IV and V.