The present invention relates to novel human hiwi protein and genes that encode such proteins. The invention is directed toward the isolation and characterization of human hiwi proteins. The invention specifically provides isolated complementary DNA copies of mRNA corresponding to a human hiwi gene. Also provided are recombinant expression constructs capable of expressing the human hiwi gene of the invention in cultures of transformed prokaryotic and eukaryotic cells, as well as such cultures of transformed cells that synthesize the human hiwi proteins encoded therein. The invention also provides methods for isolating human hematopoietic stem cells.