Succinate (or a product of succinate metabolism) is a catabolite repressor of some enzymes of the serine pathway (hydroxypyruvate reductase, serine-glyoxylate aminotransferase and glycerate kinase) but not of methanol dehydrogenase nor methylamine dehydrogenase. A mutant (PCT64) of Pseudomonas AM1, which is unable to grow on C(1) compounds, lacks glycerate kinase, showing that this enzyme is essential for the operation of the serine pathway. Mutant PCT48, unable to convert acetate into glycollate, has lost the ability to grow both on C(1) compounds and on ethanol. The properties of a third mutant (PCT57) show that Pseudomonas AM1 contains enzymes catalysing the conversion of acetate into glyoxylate. Evidence is presented that hydroxypyruvate reductase is involved in the oxidation of glycollate to glyoxylate during growth on ethanol. A scheme is proposed for the conversion of ethanol and of C(1) compounds into glyoxylate in which acetate (or a derivative) and glycollate are intermediates.

Escherichia coli IMP dehydrogenase (EC 1.2.1.14) was purified by affinity chromatography on immobilized nucleotides. The enzyme binds to agarose-bound 8-(6-aminohexyl)-AMP, N6-(6-aminohexyl)-AMP and 8-(8-amino-octyl)-IMP but not to immobilized NAD+ or Cibacron Blue F3G-A. AMP proved to be an effective eluent. A large-scale purification scheme in which 8-(6-aminohexyl)-AMP-agarose was used resulted in a homogeneous preparation of IMP dehydrogenase. The enzyme was also purified by immunoprecipitation with monospecific antisera. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, N-terminal amino acid analysis and tryptic 'finger-printing' demonstrated that IMP dehydrogenase comprises identical subunits of mol.wt. 58000. Trypsin and Pronase cleave the 58000-mol.wt. subunit into peptides of mol.wts. 42000 and 14000, with a concomitant decrease in enzyme activity. These observations rationalize much of the contradictory data on the subunit composition of the enzyme found in the literature. GMP appears to be a competitive inhibitor with respect to IMP, with no evidence for regulatory behaviour being found. The two purification procedures were also used to purify inactive mutant enzymes from guaB mutant strains of E. coli.

Pseudomonas AM1 grows on ethanol with a mean generation time of about 10h. A single alcohol dehydrogenase is responsible for oxidation of both methanol and ethanol. It is proposed that the glyoxylate bypass does not operate in Pseudomonas AM1 during growth on ethanol. Although malate synthase is present in extracts of ethanol-grown Pseudomonas AM1, the activity of isocitrate lyase is negligible. Short-term incubation experiments with [(14)C]ethanol and [(14)C]acetate indicate that a novel pathway operates during growth of Pseudomonas AM1 on ethanol. Glycollate, glyoxylate and malate are probably intermediates in this pathway.

The promoter of the gua operon has been located by transcript mapping using primer extension with reverse transcriptase. The surrounding nucleotide sequence has features characteristic of promoters under stringent and growthrate-dcpcndent regulation, namely a GC-rich discriminator next to the -10 hexarner, an upstream AT-rich sequence (the UP element) and potential FISbinding sites. Transcriptional activity of the gua promoter was examined using transcriptional fusions to lac2 placed at a single chromosomal location. Expression from gua was reduced under stringent conditions in vivo, and varied with growth rate. Growth-rate control was independent of guaninemediated repression. A fusion in which the CC-rich discriminator was mutated by insertion of an AT-rich oligonucleotide was used to demonstrate the importance of this region in control. Both stringent and growth-ratedependent controls were abolished by the mutation. Other potential regulatory signals in the vicinity of the gua promoter are a pur operator (binding site for the PurR repressor), a gua operator, a DnaA-binding site and a CRP/FNR-binding sequence, The gua promoter lies back-to-back with the promoter for xseA (exonuclease VII), the two promoters being separated by only 20 bp.

S U M M A R YR factors from Enterobacter strains isolated outside Japan were transferred to Salmonella typhimurium LT 2 and their resistance traits transduced by phage P 22. Of five$+ factors conferring resistance to tetracycline (Tc), streptomycin (Sm), sulphonamides (Su) and chloramphenicol (Cm), three, one of which conferred also resistance to kanamycin (Km), behaved like previously reported factors in that: Tc was transduced by itself but never with any other trait; all other traits were usually co-transduced; no transductants could transmit resistance by conjugation, even after infection with F'-13 lac. The other two $+ factors, which conferred also resistance to benzylpenicillin (Pn), behaved similarly, except that : Pn was transduced only at a low rate, and was never co-transduced with any other trait; and a few transductants when given F'-13 lac became able to transmit. Four $-factors, two of type Tc, Sm, Su, Pn and two of type Tc, Su, Pn differed in that : nearly all Tc transductants acquired also all the other traits; Pn was usually co-transduced with the other traits ; and some transductants could transmit by conjugation, even without F'-I 3 lac. The various transductant classes obtained by treatment with P 22 grown on LT 2 carrying both an$+ (Tc, Sm, Su, Cm, Km) and$-(Tc, Sm, Su, Pn) factor could be accounted for by transduction of fragments of either one or the other of these factors. The sorts of transductants produced by lysates of a strain possessing Tc, Sm, Su, Cm, Km determinants obtained by growing a strain carrying a n 3 + (Tc, Sm, Su, Cm) factor with one carrying an$+ (Km) factor suggested that the strain carried two $+ factors, not a recombinant factor. Both Ji-and $+ factors conferring resistance to benzylpenicillin conferred also resistance to cephalothin and cephaloridine and caused the constitutive production of a 1-lactamase, active on both benzylpenicillin and on cephalothin. All four-fi-and one of the five$+ factors resembled colI factors in that they protected strain LT 2 against the bactericidal effect of ultraviolet irradiation.