Isolation of cDNA encoding a binding protein specific to 5'-phosphorylated single-stranded DNA with G-rich sequences.

We have isolated the cDNA encoding a binding protein to the sequence motif of the immunoglobulin S mu region by the southwestern method. The binding protein designated S mu bp-2 specifically binds to 5'-phosphorylated single-stranded DNA containing 5'-G and GGGG stretches. The amino acid sequence deduced from the cDNA sequence showed that the S mu bp-2 belongs to the putative helicase superfamily which is involved in replication, recombination and repair. Expression of S mu bp-2 mRNA is ubiquitous and augmented in spleen cells stimulated with lipopolysaccharide and interleukin 4 which also induce class switching. The S mu bp-2 gene is conserved among vertebrates. Possible involvement of S mu bp-2 in class switching is discussed.