The yeast PCKl gene codmg for phosphoenolpy~vate carboxykmasc (PEPCK) was Isolated by functIona complementatlon of pckl strains from S cerevzsfae Only one copy of the gene was found per baplold yeast gcnome An RNA of about 2 kb which hybndlzed with a DNA probe mtemal to the PCKl gene was found only m cells growmg m non-fermentable carbon sources Yeast &rams carrymg multiple copies of the PCKl gene showed normal catabohte represslon of PEPCK except those carrying the shortest msertlon complementmg the mutation (2 2 kb) that presented an altered kmetlcs of derepresslon Catabohte mactlvatlon was decreased m strains transfomed with multtcopy plasmlds carrymg the PCKl gene Phosphoenolpyruvate carboxykmase, Gluconeogenesls, Catabohte repression, Catabohte mactlvatlon

The structural gene for yeast fructose-1,6-bisphosphatase (FbPase) has been cloned by complementation of a strain carrying the fbpl-1 mutation and lacking FbPase activity. By Northern analysis it could be shown that the fbpl-I mutation does not interfere with the transcription of the gene although no normal active enzyme is produced. Strains transformed with the cloned gene on a multicopy plasmid overproduce FbPase but are still subject to strong catabolite repression.Catabolite inactivation, however, is slowed down in such strains.