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