A yeast RNA binding protein that resembles the human autoantigen La.

The La protein is a 47 kDa polypeptide that frequently acts as an autoantigen in systemic lupus erythematosus and Sjögren's syndrome patients. A key property of this protein is its association with the U-rich termini of newly synthesized RNA polymerase III transcripts. Here we characterize a 32 kDa protein from Saccharomyces cerevisiae that shows sequence similarity to the N termini of vertebrate La proteins. This yeast protein also functionally resembles La in that it binds preferentially in vitro to RNAs ending with a series of U residues, and at least 53 amino acids can be deleted from the C terminus without impeding this activity. Such RNA binding activity can be detected in crude yeast extracts by immunoprecipitation of ribonucleoprotein particles by an antibody to frog La protein. However, the same antibody fails to react with the 32 kDa protein. In addition, the gene encoding this protein is not essential for viability. Together, these results suggest that additional La homologue(s) exist in yeast.