CLONING AND CHARACTERIZATION OF A NOVEL CDNA THAT IS IFN-GAMMA-INDUCED IN MOUSE PERITONEAL-MACROPHAGES AND ENCODES A PUTATIVE GTP-BINDING PROTEIN

Macrophage activation by IFN-gamma results in a cascade of gene expres sion, To identify genes activated in mouse peritoneal macrophages by I FN-gamma, we created a cDNA subtraction library of IFN-gamma-induced g enes, We have isolated from this subtraction library a novel cDNA done , called Mg21, whose mRNA is absent in unstimulated mouse peritoneal m acrophages and is induced to high levels within 4 h following the addi tion of IFN-gamma, Induction of Mg21 mRNA by IFN-gamma occurred in the presence of cycloheximide, indicating that expression of Mg21 mRNA do es not require protein synthesis, A small amount of Mg21 mRNA was also induced by LPS, but not by IL-2, IL-4, IL-10, or TNF-alpha. The DNA s equence of Mg21 is 1617 nucleotides and contains an open reading frame that codes for a protein of 415 amino acids with a predicted molecula r weight of 47,106 Da. The predicted amino acid sequence lacks a signa l sequence or transmembrane segments, indicating that the protein is a n intracellular protein, Computer search of the GenBank and EMBL datab ases indicates that this cDNA clone is unique but has 57% sequence ide ntity with IRG-47, which is a mouse gene induced by IFN-gamma in pre-B and B lymphocyte cell lines, IRG-47 encodes an intracellular protein that contains three conserved protein motifs present in GTP-binding pr oteins. Analysis of the protein sequence of Mg21 showed that these thr ee conserved protein motifs are also present in Mg21.