THE DOSE OF A PUTATIVE UBIQUITIN-SPECIFIC PROTEASE AFFECTS POSITION-EFFECT VARIEGATION IN DROSOPHILA-MELANOGASTER

A dominant insertional P-element mutation enhances position-effect var iegation in Drosophila melanogaster. The mutation is homozygous, viabl e, and fertile and maps at 64E on the third chromosome, The correspond ing gene was cloned by transposon tagging, Insertion of the transposon upstream of the open reading frame correlates with a strong reduction of transcript level, A transgene,vas constructed with the cDNA and fo und to have the effect opposite from that of the mutation, namely, to suppress variegation, Sequencing of the cDNA reveals a large open read ing frame encoding a putative ubiquitin-specific protease (Ubp). Ubiqu itin marks various proteins, frequently for proteasome-dependent degra dation. Ubps can cleave the ubiquitin part from these proteins, We dis cuss the link established here between a deubiquitinating enzyme and e pigenetic silencing processes.