Probable RNA-binding protein that specifically binds to the fourth chromosome and may bind an RNA that spreads the fourth chromosome. May be a reminiscence of X chromosome dosage compensation of ancestral Drosophila species in which the X and the fourth chromosomes are one single chromosome. Interacts with Zeste. Specifically binds to the fourth chromosome. Weakly expressed in embryos. Expression increases during larval and pupal stages. In adults, it is predominantly expressed in males, while it is weakly expressed in females.