Yeast methionine aminopeptidase type 1 is ribosome-associated and requires its N-terminal zinc finger domain for normal function in vivo.

Abstract

Methionine aminopeptidase type 1 (MetAP1) cotranslationally removes N-terminal methionine from nascent polypeptides, when the second residue in the primary structure is small and uncharged. Eukaryotic MetAP1 has an N-terminal zinc finger domain not found in prokaryotic MetAPs. We hypothesized that the zinc finger domain mediates the association of MetAP1 with the ribosomes and have reported genetic evidence that it is important for the normal function of MetAP1 in vivo. In this study, the intracellular role of the zinc finger domain in yeast MetAP1 function was examined. Wild-type MetAP1 expressed in a yeast map1 null strain removed 100% of N-terminal methionine from a reporter protein, while zinc finger mutants removed only 31-35%. Ribosome profiles of map1 null expressing wild-type MetAP1 or one of three zinc finger mutants were compared. Wild-type MetAP1 was found to be an 80S translational complex-associated protein that primarily associates with the 60S subunit. Deletion of the zinc finger domain did not significantly alter the ribosome profile distribution of MetAP1. In contrast, single point mutations in the first or second zinc finger motif disrupted association of MetAP1 with the 60S subunit and the 80S translational complex. Together, these results indicate that the zinc finger domain is essential for the normal processing function of MetAP1 in vivo and suggest that it may be important for the proper functional alignment of MetAP1 on the ribosomes.