A control reaction, in which the RT enzyme this website was omitted, was included to rule out the amplification of contaminant DNA. PCR was performed using 1 μL of the generated cDNA, and 30 PCR cycles were performed with primers F1 to F7 and R1 to R7 (Supporting information, Table S1). PCR products were visualized in a 2% agarose gel. 32P-labelled pre-tRNA substrates for RNase P and RNase Z processing assays were generated with T7 RNA polymerase from plasmids pSer, pYSR and pNQQ (Fig. 2). These plasmids

contain, in pUC19, the indicated pre-tRNA(s) obtained by PCR from genomic DNA with appropriate oligonucleotides (Table S1) cloned downstream of a T7 promoter. For run-off in vitro transcription, pSer and pNQQ were digested with HindIII, and pYSR was digested with NruI. RNA subunit of RNase P (P RNA) from Anabaena 7120 was obtained by in vitro transcription as described (Pascual

& Vioque, 1999). The gene encoding Anabaena 7120 protein subunit of RNase P (P protein) (alr3413) was amplified by PCR with oligonucleotides all3413F1 and all3413R1 (Table S1) from Anabaena 7120 genomic DNA and cloned into pET28 (Novagen) in phase with a hexahistidine tag at the amino end. The protein was overexpressed in BL21(DE3) cells and purified by chromatography on a HiTrap chelating column followed by HiTrap CM-Sepharose column (GE Healthcare). Ipilimumab in vivo RNase P holoenzyme was reconstituted as described for the Synechocystis enzyme (Pascual & Vioque, 1996). RNase P assays were performed under single turnover conditions essentially as described (Pascual & Vioque, 1999). Synechocystis almost RNase Z was purified and assayed as described (Ceballos-Chávez & Vioque, 2005). To identify aminoacylated tRNAs, we used the OXOPAP assay (Gaston et al., 2008). Briefly, RNA was isolated from Anabaena 7120 under acidic conditions as described previously, and 5 μg of total RNA was treated with sodium m-periodate to oxidize the 3′ ends of free

tRNAs. Subsequently, the samples were deacylated, resulting in a population in which only aminoacylated tRNAs carry a 3′-OH suitable for polyadenylation. The samples were then polyadenylated and analysed by RT-PCR with an oligoT anchor (OXOPAPRTR) and oligos specific for each of the tRNAs being analysed (Table S1). A control reaction was always included, in which aminoacyl-tRNAs were deacylated before oxidation and therefore were not suitable for polyadenylation and RT-PCR. The trnS-GCU(1) and trnS-GCU(2) genes were amplified by PCR from Anabaena 7120 and cloned in pGEM-T and pUC19 vectors, respectively. Both vectors were digested with MvaI (Takara) to produce a linear template for transcription with T7 RNA polymerase that generates the mature full-length tRNA containing the 3′ CCA sequence. Transcription was carried out in 50 μL as described (Pascual & Vioque, 1999).