YB-1 cDNA clones were isolated by binding site screening of a Hela expression library using a human papillomavirus type 18 enhancer oligonucleotide. YB-1 belongs to a family of transcription factors which bind to recognition sequences containing a core CCAAT element. YB-1 bound to its single stranded recognition sequence on the sense strand but not to the anti-sense strand. A synthetic peptide antiserum derived from the predicted YB-1 amino acid sequence identified a 42kD nuclear protein in immunoblots. A protein with the same size was detected by binding site blotting experiments using the HPV18 enhancer oligonucleotide which bound YB-1. YB-1 gene expression was restricted in tissues from a human 24 week old fetus. High levels of YB-1 mRNA were present in heart, muscle, liver, lung, adrenal gland and the brain, in contrast, low amounts of YB-1 mRNA were found in thymus, kidney, bone marrow and spleen. In pancreas, bladder, stomach and testis YB-1 mRNA could not be detected by Northern hybridization. Finally, we have identified four YB-1 related loci in the mouse genome and have mapped these loci to four different mouse chromosomes by interspecific backcross analysis.
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