STP1, a gene involved in pre-tRNA processing, encodes a nuclear protein containing zinc finger motifs

STP1 is an unessential yeast gene involved in the removal of intervening sequences from some, but not all, families of intervening sequence-containing pre-tRNAs. Previously, we proposed that STP1 might encode a product that generates pre-tRNA conformations efficiently recognized by tRNA-splicing endonuclease. To test the predictions of this model, we have undertaken a molecular analysis of the STP1 gene and its products. The STP1 locus is located on chromosome IV close to at least two other genes involved in RNA splicing: PRP3 and SPP41. The STP1 open reading frame (ORF) could encode a peptide of 64,827 Da; however, inspection of putative transcriptional and translational regulatory signals and mapping of the 5' ends of mRNA provide evidence that translation of the STP1 ORF usually initiates at a second AUG to generate a protein of 58,081 Da. The STP1 ORF contains three putative zinc fingers. The first of these closely resembles both the DNA transcription factor consensus and the Xenopus laevis p43 RNA-binding protein consensus. The third motif more closely resembles the fingers found in spliceosomal proteins. Employing antisera to the endogenous STP1 protein and to STP1-LacZ fusion proteins, we show that the STP1 protein is localized to nuclei. The presence of zinc finger motifs and the nuclear location of the STP1 protein support the model that this gene product is involved directly in pre-tRNA splicing.