title: Isolation, characterization, and mapping of Escherichia coli mutants blocked in the synthesis of ornithine decarboxylase.
abstract: Several Escherichia coli K-12 mutants blocked in the synthesis of ornithine decarboxylase (OD) were isolated after transduction for serA+ in a strain (MA197) blocked in agmatine ureohydrolase (AUH) with a mutagenized phage lysate of P1. The new double-polyamine mutants were characterized by an unconditional polyamine dependence; either putrescine or spermidine was required for normal growth. The mutational block was varified by the demonstration of a virtual absence of OD activity in cellular extracts. The mutation, designated speC, was mapped by P1 transduction in several strains and was shown to have a cotransduction frequency of 17.2% with serA. Map order was established as serA speB speC metK. A derivative of one of the OD mutants having wild-type levels of AUH and blocked in OD was utilized along with an OD AUH mutant and an OD+ AUH strain to explore the phenomenon of "pathway selection" using growth rate as a parameter. Polyamine pool studies were carried out simultaneously. The results presented here support the hypothesis of pathway selection, implying a preferential utilization of exogenous arginine rather than endogenously produced arginine in polyamine biosynthesis.
mesh_terms: D000376:Agmatine; D001120:Arginine / Q000378:metabolism; D002262:Carboxy-Lyases / Q000096:biosynthesis*; D002474:Cell-Free System; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism; D009154:Mutation; D009955:Ornithine Decarboxylase / Q000096:biosynthesis* / Q000378:metabolism; D011700:Putrescine / Q000378:metabolism; D013095:Spermidine / Q000378:metabolism; D014161:Transduction, Genetic; D014512:Ureohydrolases / Q000378:metabolism
chemical_list: D000376:Agmatine; D001120:Arginine; D014512:Ureohydrolases; D002262:Carboxy-Lyases; D009955:Ornithine Decarboxylase; D013095:Spermidine; D011700:Putrescine