Mutation in P0, a dual function ribosomal protein/apurinic/apyrimidinic endonuclease, modifies gene expression and position effect variegation in Drosophila

In a search for modifiers of gene expression with the white eye color gene as a target, a third chromosomal P-element insertion mutant l(3)01544 has b een identified that exhibits a strong pigment increase in a white-apricot b ackground. Molecular analysis shows that the P-element insertion is found i n the first intron of the gene surrounding the insertion site. Sequencing b oth the cDNA and genomic fragments revealed that the identified gene is ide ntical to one encoding ribosomal protein P0/apurinic/apyrimidinic endonucle ase. The P-element-induced mutation, l(3)01544, affects the steady-state le vel of white transcripts and transcripts of some other genes. In addition, l(3)01544 suppresses the variegated phenotypes of In(1)w(m4h) and In(1)y(3P ), suggesting a potential involvement of the PO protein in modifying positi on effect variegation. The revertant generated by the precise excision of t he P element has lost all mutant phenotypes. Recent work revealed that Dros ophila ribosomal protein PO contains an apurinic/apyrimidinic endonuclease activity. Our results suggest that this multifunctional protein is also inv olved in regulation of gene expression in Drosophila.