Poly(ADP-ribose) polymerase interacts with novel Drosophila ribosomal proteins, L22 and L23a, with unique histone-like amino-terminal extensions

Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme that recognizes and binds to the nicks and ends of DNA, and catalyses successive ADP-ribosylati on reactions. To clarify the function of PARP at the molecular level, we se arched proteins which interact with PARP. In the auto-modification domain o f PARP in Drosophila, there is a putative leucine-zipper motif which can in teract with other protein molecules. To find interacting proteins we examin ed the auto-modification domain of Drosophila PARP, using the Far-Western s creening method. From six independent cDNA clones isolated, we characterize d two clones, PBP-3 and PBP-12. The predicted amino acid sequences from 109 to 269 of PBP-3 and from 184 to 312 of PBP-12 had more than 62% identities to mammalian L23a (rp123a) and L22 (rp122), the ribosomal proteins of the large subunit. This indicated that PBP-3 and PBP-12 are Drosophila homologu es of L23a and L22, respectively. These Drosophila ribosomal protein L22 an d L23a have additional Ala-, Lys- and Pro-rich sequences at the amino termi nus, which have a resemblance to the carboxy-terminal portion of histone H1 . Thus, Drosophila L22 and L23a might have two functions, namely the role o f DNA-binding similar to histone H1 and the role of organizing the ribosome . (C) 1999 Elsevier Science B.V. All rights reserved.