Human MOB is a novel gene first cloned in lung tissue and lymphoma tissue. It is proposed to express predominately in brain, and be a five-pass transmembrane protein. A new expressed sequence tag (EST) (GenBank accession number: BI740300) matched completely with human MOB gene was obtained. The 2 230 bp sequence of human MOB cDNA, which contains a 1 242 bp (nt 415～1 656) open reading frame, encoding a protein of 413 amino acid residues, was successfully cloned. In addition, rat and chicken MOB cDNA sequences, which also contain a 1 242 bp open reading frame, were cloned in silico by aligning dozens of overlapping rat and chicken ESTs and cDNA sequences identified from GenBank. Human MOB was mapped on chromosome 10q11.1～11.2. Homology searches with the deduced 413 amino acid residues revealed human MOB shares 97% similarity with murine MOB, 97% with rat MOB, 91% with chicken MOB and 45%～73% with lots of hypothetical proteins of various origin. The predicted protein contains SAM domain, which has been suggested to be an evolutionarily conserved protein-binding domain that is involved in the regulation of numerous developmental processes in diverse eukaryotes and can potentially function as a protein interaction module through its ability to homo- and heterooligomerise with other SAM domains. Homology searches and domain query indicate that human MOB is a member of potential phylogenetically conserved MOB family. RT-PCR revealed that human MOB was almost expressed in all kinds of tissues and cells, which is completely consistent with the in silico expression pattern identified by bioinformatics analysis. In contrast to bioinformatics analysis and previous study, however, human MOB has widespread subcelluar expression, primarily in nuclei. Further study in HeLa cells shows that overexpression of human MOB seems not to influence cell cycle and apoptosis.Taken together, human MOB is a novel phylogenetically conserved gene, which is proposed to express in almost all tissues and cells, and has widespread subcelluar expression, primarily in nuclei. It may play a role in signal transduction and thus be involved in development regulation, but seems not to influence cell cycle and apoptosis. Further investigation remains needed.