Telomeres the physical ends of eukaryotic chromosomes are transcribed into telomeric repeat-containing RNA (TERRA) a BINA large non-coding RNA which forms an integral part of telomeric heterochromatin. with telomerase activity. Finally it has been proposed that a switch at telomeres from replication protein A (RP-A) for DNA replication in S phase to protection of telomeres 1 (POT1)/TPP1 after S phase is triggered by hnRNPA1 and TERRA (23). telomerase activity is maintained as long as the levels of TERRA and hnRNPA1 are balanced. Thus TERRA and hnRNPA1 may provide a bimolecular switch to fine-tune telomerase activity at chromosome ends. MATERIALS AND METHODS Plasmids and oligonucleotides Plasmids for transient transfection of human telomerase reverse transcriptase (hTERT) (pcDNA6-ZZ-3xFlag-hTERT) and hTR (pBS-U1-hTR) were described previously (25). For bacterial expression of hnRNPA1 pGEX-hnRNPA1 was generated by PCR amplification of the hnRNPA1 open reading frame from pcDNA6-hnRNPA1 using BamH1-A1_F and A1-EcorRI_R primers (Supplementary Table S1) and subcloned into the BamHI and EcoRI sites of pGEX-6P-1 vector (GE Healthcare). pcDNA6-hnRNPA1 was generated by PCR amplification of the hnRNPA1 open reading frame from pCMV6-XL5-hnRNPA1 (Origene clone “type”:”entrez-nucleotide” attrs :”text”:”NM_002136″ term_id :”83641893″ term_text :”NM_002136″NM_002136) using HindIII-A1_F and EcoRI-A1_R primers. cDNAs were subcloned into retroviral-based pCL vectors for expression of ZZ or hnRNPA1-ZZ proteins in HT1080 cells. Oligonucleotides were purchased from Microsynth and are listed in Supplementary Table S1. Antibodies Antibodies against Flag (F1804) and tubulin (T9026 for western blotting) were obtained from Sigma. The 9B11 antibody against Myc was purchased from Cell Signaling. Antibodies against hnRNPA1 (SC-32B01) tubulin (SC-8035 for immunoprecipitation) cyclin E (SC-247) and cyclin B1 (SC-245) were from Santa Cruz and antibodies against GST (27457701) were from BINA GE Healthcare. Stable cell line generation HT1080 stable cell lines were generated by viral transduction and puromycin selection (1 μg/ml). hnRNPA1 depletion The 293T cells were transfected for 48 h with siRNAs against GFP or hnRNPA1 (sequences in Supplementary Table S1) using Interferin (Polyplus). Protein expression and purification Rosetta pLysS competent bacteria (Novagen) were transformed with pGEX-hnRNPA1. For expression of recombinant GST-hnRNPA1 2 l of 2YT containing 34 μg/ml chloramphenicol 50 μg/ml ampicillin and 50 μg/ml carbenicillin were inoculated with 50 ml of overnight culture and incubated at 37°C until the OD600 reached 0.8. Protein expression was induced for 3 h at 37°C by adding 0.4 mM IPTG. After centrifugation the bacteria were washed once with ice-cold 1x PBS. The pellet was resuspended in 60 ml lysis buffer (1x PBS 1 mM DTT and 1x protease inhibitor cocktail EDTA-free from Roche). The lysate was sonicated five times for 10 s (Branson BINA sonifier 250 setting 3 constant). Glycerol and Triton X-100 were added to final concentrations of 10 (v/v) and 1% (v/v) respectively. The extract was incubated on a rotating wheel for 15 min at room temperature and then centrifuged for 15 min at 12 000 at 4°C. The supernatant was incubated with 2 ml 50% slurry of GSH-coupled beads (GE Healthcare). After binding for 2 h at 4°C bead-bound proteins were washed once with 1x PBS 10 (v/v) glycerol and three times with 1xPBS. GST-hnRNPA1 was eluted for 30 min at 4°C with 2 ml 20 mM NaCl 20 mM GSH and 200 mM Tris-HCl (pH 9.5). Glycerol was added to a final concentration of 10% (v/v). To remove the remaining beads the eluate was passed through a 35 μM filter (Mobitec). The same protocol was applied to express and purify GST alone using BINA pGEX-6P-1 vector with the only exception that the elution steps were performed with 20 mM GSH and 200 mM Tris-HCl (pH 7.5). The second LIMK1 purification step was performed on a HiTrapQ HP 1 ml column using the Akta purifier system and the Unicorn software (GE Healthcare). Before loading each eluate from the first purification step was diluted 10x in 20 mM Tris-HCl (pH 8.0) and 25 mM NaCl. A 20 ml NaCl gradient was applied from BINA 25 mM to 1 1 M. 500 μl fractions were collected glycerol was added to 10% (v/v) final concentration and samples were quick-frozen. Telomerase purification For telomerase overexpression Human.