MOLECULAR-CLONING OF MSSP-2, A C-MYC GENE SINGLE-STRANDED BINDING-PROTEIN - CHARACTERIZATION OF BINDING-SPECIFICITY AND DNA-REPLICATION ACTIVITY

We have previously reported the human cDNA encoding MSSP-1, a sequence -specific double- and single-stranded DNA binding protein [Negishi, Ni shita, Saegusa, Kakizaki, Galli, Kihara, Tamai, Miyajima, Iguchi-Ariga and Ariga (1994) Oncogene, 9, 1133-1143]. MSSP-1 binds to a DNA repli cation origin/transcriptional enhancer of the human c-myc gene and has turned out to be identical with Scr2, a human protein which complemen ts the defect of cdc2 kinase in S.pombe [Kataoka and Nojima (1994) Nuc leic Acid Res., 22, 2687 - 2693]. We have cloned the cDNA for MSSP-2, another member of the MSSP family of proteins. The MSSP-2 cDNA shares highly homologous sequences with MSSP-1 cDNA, except for the insertion of 48 bp coding 16 amino acids near the C-terminus. Like MSSP-1, MSSP -2 has RNP-1 consensus sequences. The results of the experiments using bacterially expressed MSSP-2, and its deletion mutants, as histidine fusion proteins suggested that the binding specificity of MSSP-2 to do uble- and single-stranded DNA is the same as that of MSSP-1, and that the RNP consensus sequences are required for the DNA binding of the pr otein. MSSP-2 stimulated the DNA replication of an SV40-derived plasmi d containing the binding sequence for MSSP-1 or -2. MSSP-2 is hence su ggested to play an important role in regulation of DNA replication.