A HUMAN GENE ENCODING A PUTATIVE BASIC HELIX-LOOP-HELIX PHOSPHOPROTEIN WHOSE MESSENGER-RNA INCREASES RAPIDLY IN CYCLOHEXIMIDE-TREATED BLOODMONONUCLEAR-CELLS

G0S8 is a member of a set of putative G0/G1 switch regulatory genes (G OS genes) selected by screening cDNA libraries prepared from blood mon onuclear cells cultured for 2 hr with lectin and cycloheximide. Compar ison of a full-length cDNA sequence with the corresponding genomic seq uence reveals an open reading frame of 211 amino acids, distributed ac ross 5 exons. The 24-kD protein has a basic domain preceding a potenti al helix-loop-helix domain which contains a QTK motif found about 60 a mino acids from the carboxyl terminus in the loop region of several he lix-loop-helix proteins. There are potential phosphorylation sites for protein kinase C, creatine kinase II, and protein tyrosine kinases an d regions of sequence similarity to helix-loop-helix proteins, tyrosin e phosphatases, and RNA and DNA polymerases. The genomic sequence cont ains a CpG island, suggesting expression in the germ line. Potential b inding sites for transcription factors are present in the 5' flank and introns; these include Zif268/NGFI-A/EGR1/G0S30, NGFI-B, Apl, and fac tors that react with retroviral long terminal repeats (LTRs). There ar e several potential interferon response elements and a serum response element in the 3' flank overlapping a region of similarity to a cytome galovirus immediate-early gene enhancer. Many of these motifs are foun d in immediate-early G0/G1 switch genes; however, we were unable to de monstrate an increase in G0S8 mRNA in response to lectin alone. Sequen ce similarities are noted between G0S8 and a variety of genes involved in the immune system, in the regulation of retroviruses, and in the c ell cycle.