A SYSTEM FOR STUDYING THE SPECIFICITY OF SERYLATION WITH YEAST SERYL-TRANSFER-RNA SYNTHETASE

Serylation is the covalent attachment of serine to a serine specific t RNA. It is catalyzed by the seryl-tRNA synthetase (SerRS). There are p resumably two seryl-tRNA synthetases, encoded by different nuclear gen es, that perform the serylation task in Saccharomyces cerevisiae. One works in the cytoplasm and the other in mitochondria. The gene for the cytoplasmic enzyme has been cloned, sequenced and can be functionally expressed both in yeast and in Escherichia coli. Its protein product is a 106 kD homodimer, which can be easily purified from bacterial and yeast overproducing strains. The enzyme recognizes six tRNA(Ser) isoa cceptors and selenocysteine tRNA in yeast, as well as several non homo logous tRNAs from prokaryotic and eukaryotic sources. By combining gen etic and biochemical methods, a system for studying the recognition be tween yeast seryl-tRNA synthetase and tRNA substrates, both in vivo an d in vitro, has been designed.