Accurate 3 ' end processing and adenylation of human signal recognition particle RNA and Alu RNA in vitro

Human signal recognition particle (SRP) RNA is transcribed by RNA polymeras e III and terminates with -GU-CUCUCTUUOH on its 3' end. Our previous studie s showed that the three terminal uridylic acid residues of human SRP RNA ar e post-transcriptionally removed and a single adenylic acid residue is adde d, resulting in a 3' end sequence of-GUCUCUA(OH) (Sinha, K.M., Gu, J., Chen . Y., and Reddy, R. (1998) J. Biol, Chem, 273, 6853-6859), In this study we show that the Alu RNA, corresponding to the 5' and 3' ends of SRP RNA, is also accurately processed and adenylated in vitro. Alu RNAs containing 7 or II additional nucleotides on the 3' end were accurately processed and then adenylated, Deletion analysis showed that an 87-nucleotide-long motif comp rising of the 5' and 3' ends, including stem IV of the Alu RNA, is sufficie nt and necessary for the 3' end processing and adenylation, A 73-nucleotide -long construct with deletion of stem IV, required for the binding of SRP 9 /14-kDa proteins, was neither processed nor adenylated, The adenylated Alu RNA as well as adenylated SRP RNA were bound to the SRP 9/14-kDa heterodime r and were immunoprecipitated by specific antibodies. A significant fractio n of SRP RNA in the nucleoli was found to be processed and adenylated. Thes e data are consistent with nascent SRP and/or Alu RNAs first binding to SRP 9/14-kDa protein heterodimer, followed by the removal of extra sequence on the 3' end and then the addition of one adenylic acid residue in the nucle us, before transport into the cytoplasm.