Actually, this is kinda funny -- the gene isn't perl, but rather "Per One", it's just that the 1 and l look the same in the font in that article. Per1 is the symbol for Period Homolog 1, a PAS family protein first identified in drosophila (fruit fly). The period series of genes (two in higher eukaryotes, I think) are critical clock proteins, important for setting circadian rhythm.