Two highly homologous ribonuclease genes expressed in mouse eosinophils identify a larger subgroup of the mammalian ribonuclease superfamily.
Two putative ribonucleases have been isolated from the secondary granules of mouse eosinophils. Degenerate oligonucleotide primers inferred from peptide sequence data were used in reverse transcriptase-PCR reactions of bone marrow-derived cDNA. The resulting PCR product was used to screen a C57BL/6J bone marrow cDNA library, and comparisons of representative clones showed that these genes and encoded proteins are highly homologous (96% identity at the nucleotide level; 92/94% identical/similar at the amino acid level). The mouse proteins are only weakly homologous (approximately 50% amino acid identity) with the human eosinophil-associated ribonucleases (i.e., eosinophil-derived neurotoxin and eosinophil cationic protein) and show no sequence bias toward either human protein. Phylogenetic analyses established that the human and mouse loci shared an ancestral gene, but that independent duplication events have occurred since the divergence of primates and rodents. The duplication event generating the mouse genes was estimated to have occurred < 5 x 10(6) years ago (versus 30 to 40 x 10(6) years ago in primates). The identification of independent duplication events in two extant mammalian orders suggests a selective advantage to having multiple eosinophil granule ribonucleases. Southern blot analyses in the mouse demonstrated the existence of three additional highly homologous genes (i.e., five genes total) as well as several more divergent family members. The potential significance of this observation is the implication of a larger gene subfamily in primates (i.e., humans).
Department of Biochemistry and Molecular Biology, Mayo Clinic, Scottsdale, AZ 85259, USA.
K A
KA
Larson
E V
EV
Olson
B J
BJ
Madden
G J
GJ
Gleich
N A
NA
Lee
J J
JJ
Lee
D000595:Amino Acid Sequence; D000818:Animals; D001798:Blood Proteins / Q000235:genetics; D015139:Blotting, Southern; D002417:Cattle; D002645:Chickens; D003001:Cloning, Molecular; D003594:Cytoplasmic Granules / Q000201:enzymology; D047091:Eosinophil Granule Proteins; D047208:Eosinophil-Derived Neurotoxin; D004804:Eosinophils / Q000201:enzymology*; D006071:Gorilla gorilla; D006801:Humans; D008252:Macaca fascicularis; D051379:Mice; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000235:genetics; D002679:Pan troglodytes; D010802:Phylogeny; D011148:Pongo pygmaeus; D011894:Rana pipiens; D051381:Rats; D012259:Ribonuclease, Pancreatic / Q000235:genetics; D012260:Ribonucleases / Q000737:chemistry / Q000235:genetics*; D012452:Saguinus; D016415:Sequence Alignment; D013552:Swine
D001798:Blood Proteins; D047091:Eosinophil Granule Proteins; D009498:Neurotoxins; D047208:Eosinophil-Derived Neurotoxin; D012260:Ribonucleases; D012259:Ribonuclease, Pancreatic