The determination of base sequences of several transfer ribonucleic acids has led to proposals for their secondary structure. The most popular structural model has had the form of a cloverleaf.' There have also been some indications of an additional fixation of the arms of the model in a tertiary structure. So far there is no direct experimental proof for any of these structures, although inves...

Levels of pyruvate carboxylase (PC), phosphopyruvate carboxylase (PEPC), and malate dehydrogenase (decarboxylating) were compared in wild-type bakers' yeast (I), a cytoplasmic-respiratory mutant (II), a biotin-deficient wild-type yeast (III), and a biotin-deficient respiratory mutant (IV). PC activities were greatly reduced in III and IV, whereas PEPC was reduced in II and IV. Malate dehydrogen...

Recent investigations by Ehrensviird et al. (1) have revealed that the carbon skeleton of aspartic acid in Torula yeast can arise readily from administered acetate. With C1aH&“OOH, the aspartic acid formed during growth contained Cl4 equally distributed between the two carboxyl groups, and most of the C** equally distributed between the 2 central carbon atoms. In the preceding papers (2, 3) the...