Human YBX1 and YBX3 interact with mt tRNAs. (A) Small RNAs associated with YBX1 and YBX3. HeLa cellular RNAs coimmunopurified with endogenous or transiently expressed HA- and Flag-tagged YBX1 and YBX3 were 3′ end-labeled and analyzed on 6% sequencing gels. Control IPs with nonimmune sera (cont IP) or from nontransfected cell extracts (NT) are shown. The 7SK snRNA and YBX1-associated mt tRNAs identified by direct chemical sequencing are indicated. (Lanes M) Size markers in nucleotides. (B) Western blot analyses. IP of HeLa endogenous and transiently expressed epitope-tagged YBX1 and YBX3 was confirmed by YBX1- and YBX3-specific antibodies. (Ext) HeLa cell extracts. Positions of marker proteins are indicated. (C) Copurification of HeLa mt tRNAs with YBX1 and YBX3 was measured by northern blot analyses with sequence-specific oligonucleotide probes. IP of YBX1 and YBX3 was confirmed by western blotting. (Ext) HeLa cell extract (50× dilution). (Lane M) Size markers.
