The poly(A)-binding protein Nab2 functions in RNA polymerase III transcription

RNA polymerase III (RNAPIII) synthesizes most small RNAs, the most prominent being tRNAs. Although the basic mechanism of RNAPIII transcription is well understood, recent evidence suggests that additional proteins play a role in RNAPIII transcription. Here, we discovered by a genome-wide approach that Nab2, a poly(A)-binding protein important for correct poly(A) tail length and nuclear mRNA export, is present at all RNAPIII transcribed genes. The occupancy of Nab2 at RNAPIII transcribed genes is dependent on transcription. Using a novel temperature-sensitive allele of NAB2, nab2-34, we show that Nab2 is required for the occupancy of RNAPIII and TFIIIB at target genes. Furthermore, Nab2 interacts with RNAPIII, TFIIIB, and RNAPIII transcripts. Importantly, impairment of Nab2 function causes an RNAPIII transcription defect in vivo and in vitro. Taken together, we establish Nab2, an important mRNA biogenesis factor, as a novel player required for RNAPIII transcription by stabilizing TFIIIB and RNAPIII at promoters.