gcr is a mutation considerably decreasing the assayed amounts of most glycolysis enzymes in Saccharomyces cerevisiae (Clifton, D., Weinstock, S. B., and Fraenkel, D. G. (1978) Genetics 88, 1-11). We show here that although in the wild type strain the amounts of these enzymes do not greatly differ between cells from different media, in the gcr mutant strain most of the enzyme amounts are 5% or less, relative to wild type, from cells grown without sugars, but 20-50% from cells grown with sugars. Lower relative values were found for phosphoglycerate mutase and enolase. A corresponding alteration in the mutant in the intensities of several major protein bands could even be seen in stained gels after electrophoresis of crude extracts: the profiles were otherwise normal. Results of titration of phosphoglycerate kinase with antibody accorded with activity. Transfer of cells between the two types of media did not lead to a more rapid adjustment of enzyme amounts than expected from the steady state levels. gcr is not allelic to GPM (the gene for phosphoglycerate mutase) or to RNA1 (which affects transport of RNA from the nucleus). Translation of total RNA in a rabbit reticulocyte lysate gave a pattern of polypeptides similar to the in vivo one. Thus, gcr is likely to affect somehow mRNA synthesis or lifetime for a discrete number of proteins.