Observations on amino acid-dependent exchanges of inorganic pyrophosphate and ATP

Moments of Discovery

Devoted teachers and mentors during early childhood and adolescence nurtured my ambition to become a scientist, but it was not until I actually began doing experiments in college and graduate school that I was confident about that choice and of making it a reality. During my postdoctoral experiences and thereafter, I made several significant advances, most notably the discovery of the then novel acyl- and aminoacyl adenylates: the former as intermediates in fatty acyl coenzyme A (CoA) formation and the latter as precursors to aminoacyl tRNAs. In the early 1970s, my research changed from a focus on transcription and translation in Escherichia coli to the molecular genetics of mammalian cells. To that end, my laboratory developed a method for creating recombinant DNAs that led us and others, over the next two decades, to create increasingly sophisticated ways for introducing “foreign” DNAs into cultured mammalian cells and to target modifications of specific chromosomal loci. Circumstances surrounding that work drew me into the public policy debates regarding recombinant DNA practices. As an outgrowth of my commitment to teaching, I coauthored several textbooks on molecular genetics and a biography of George Beadle. The colleagues, students, and wealth of associates with whom I interacted have made being a scientist far richer than I can have imagined.

A cytochemical study on the pancreas of the guinea pig. IV. Chemical and metabolic investigation of the ribonucleoprotein particles

Five ribonucleoprotein (RNP) fractions were isolated from the postmitochondrial supernatant of the pancreas of the guinea pig. Two were obtained from the microsomes which, by deoxycholate (DOC) treatment, were subdivided into a DOC-soluble and a DOC-insoluble fraction. The latter was taken to represent attached RNP particles. Two other fractions obtained from the microsomal supernatant supposedly represent free RNP particles existing as such in the cytoplasm, while a third fraction resisted sedimentation for 20 hours at 105,000 g and is considered to be a soluble nucleoprotein. These fractions exhibited different RNA/protein ratios and also different RNA turnover patterns, as determined after in vivo labelling with adenine-8-C¹⁴. However, little discernible differences could be detected in the nucleotide composition of the RNA moieties of these RNP fractions. Amino acid-"activating" enzymes were found to occur in the fraction containing the soluble nucleoproteins. The discussion focuses on the relationships between these fractions and protein synthesis in the pancreas, using data given in this and a previous paper, and data contained in the literature.

GLYCYL-RNA SYNTHETASE OF RAT LIVER: PARTIAL PURIFICATION AND EFFECTS OF SOME METAL IONS ON ITS ACTIVITY

Glycyl-RNA synthetase has been purified 40-fold from a 105,000 × g supernatant of an homogenate of rat liver by successive precipitation at pH = 5.0, heat treatment at 55 °C for 3.0 minutes in the presence of 1.0 mM ATP, and ammonium sulphate fractionation. The purified fractions catalyzed glycine-dependent ATP-32PP exchange. The effect of some metal ions on glycine activation was studied. Activation occurred in the presence of either Mg++or Mn++. The apparent stimulation of glycine activation by Co++was found to be an artifact.

GLYCYL-RNA SYNTHETASE OF RAT LIVER: PARTIAL PURIFICATION AND EFFECTS OF SOME METAL IONS ON ITS ACTIVITY

Glycyl-RNA synthetase has been purified 40-fold from a 105,000 × g supernatant of an homogenate of rat liver by successive precipitation at pH = 5.0, heat treatment at 55 °C for 3.0 minutes in the presence of 1.0 mM ATP, and ammonium sulphate fractionation. The purified fractions catalyzed glycine-dependent ATP-32PP exchange. The effect of some metal ions on glycine activation was studied. Activation occurred in the presence of either Mg++or Mn++. The apparent stimulation of glycine activation by Co++was found to be an artifact.