 "Rad9" was originally found in budding yeast cells but a human homolog has also been found and studies have suggested that the molecular mechanisms of the S and G2 checkpoints are conserved in eukaryotes.Thus, what is found in yeast cells are likely to be similar in human cells.This gene product is highly similar to S. pombe rad9, a cell cycle checkpoint protein required for cell cycle arrest and DNA damage repair in response to DNA damage.