Drosophila RNase Z^L is involved in cell growth and cell cycle progression. Xie Xie, Edward Dubrovsky. Biological Sciences, Fordham University, Bronx, NY.

   The RNase Z enzyme is a highly conserved endoribonuclease expressed in all living cells. Previously, we reported the identification and biochemical analysis of dRNaseZ, the Drosophila homolog of the long form of dRNase Z^L. Knockdown of dRNaseZ by RNAi impaired larval growth and development causing death during the second larval molt. To clarify further the role of dRNaseZ in fly development, we have now isolated and characterized the knockout allele, RNZ^ED24. KO flies can be rescued by a dRNaseZ-expressing transgene controlled by UAS, HS, or native promoters. Using fully functional V5-tagged genomic transgene, we followed the expression of dRNaseZ at the protein level, and found dRNaseZ is highly abundant in dividing cells. By utilizing a conditional rescue system, we studied the requirement of dRNaseZ in adult stage and found dRNaseZ KO affect flies fertility. Combining FLP/FRT technique and conditional rescue system, we found RNaseZ is required for cell growth in endoreplicating tissue. RNaseZ KO affects protein synthesis through tRNA nuclear accumulation. While in mitotic tissues, RNaseZ is required for cell proliferation. RNaseZ KO cells are arrested at G2/M transition. We therefore conclude that dRNaseZ protein is required for endoreplicating cell growth and mitotic cell proliferation.