2 NOVEL HUMAN MEMBERS OF AN EMERGING MAMMALIAN GENE FAMILY RELATED TOMONO-ADP-RIBOSYLATING BACTERIAL TOXINS

Mono-ADP-ribosylation is one of the posttranslational protein modifica tions regulating cellular metabolism, e.g., nitrogen fixation, in prok aryotes. Several bacterial toxins mono-ADP-ribosylate and inactivate s pecific proteins in their animal hosts, Recently, two mammalian GPI-an chored cell surface enzymes with similar activities were cloned (desig nated ART1 and ART2), We have now identified six related expressed seq uence tags (ESTs) in the public database and cloned the two novel huma n genes hom which these are derived (designated ART3 and ART4). The de duced amino acid sequences of the predicted gene products show 28% seq uence identity to one another and 32-41% identity vs the muscle and T cell enzymes. They contain signal peptide sequences characteristic of GPI anchorage. Southern Zoo blot analyses suggest the presence of rela ted genes in other mammalian species. By PCR screening of somatic cell hybrids and by in situ hybridization, we have mapped the two genes to human chromosomes 4p14-p15.1 and 12q13.2-q13.3. Northern blot analyse s show that these genes are specifically expressed in testis and splee n, respectively, Comparison of genomic and cDNA sequences reveals a co nserved exon/intron structure, with an unusually large exon encoding t he predicted mature membrane proteins. Secondary structure prediction analyses indicate conserved motifs and amino acid residues consistent with a common ancestry of this emerging mammalian enzyme family and ba cterial mono(ADP-ribosyl)transferases. It is possible that the four hu man gene family members identified so far represent the ''tip of an ic eberg,'' i.e., a larger family of enzymes that influences the function of target proteins via mono-ADP-ribosylation. (C) 1997 Academic Press .