John D. Karkas

Studies on the specification of accessory biochemical characters, as exemplified by the fatty acid patterns of various strains of Escherichia coli.

Abstract 1. 1. In an attempt to gain some insight into the manner in which the genome of microbial cell may be concerned with the specification of accessory biochemical characters, the quantitative distribution of the principal fatty acids in various strains and mutants of Escherichia coli was investigated by means of gas-liquid chromatography of the methyl esters. 2. 2. The wild types of strains B, K12, and 15 differed distinctly in their fatty acid patterns, both in minimal and in complete medium and after different periods of growth. 3. 3. Several of the mutants examined, including a series of streptomycin-resistant variants, did not differ in this respect appreciably from the parent strains. 4. 4. Nine methionine auxotrophs exhibited, however, characteristically different patterns when compared with the corresponding wild-type strains. The addition of various concentrations of methionine to the minimal medium, though permitting the normal rate of growth of the auxotrophs, did not abolish the differences in the fatty acid profiles. 5. 5. When the DNA of a thymine-requiring mutant of E. coli 15 was made to incorporate the thymine-analogue 5-bromouracil, a characteristic change in the fatty acid pattern resulted which was more expressed after the replication of the cells containing the halopyramidine. 6. 6. The paper concludes with a discussion, in more general terms, of the problem of the rigid control, in certain instances, of quantitative and substituent patterns.

A new method of assay for polynucleotide ligase

Abstract A new method for the assay of polynucleotide ligase is described. It consists of two parallel DNA polymerase reactions with poly(dA) · oligo(dT) as template-primer and d[3H] TTP as precursor; ligase is added to both, but one is supplemented with NMN and the other with NAD. In the presence of NAD, ligase joins several oligo(dT) molecules, thus reducing the number of primer sites available to the polymerase, while the NMN-supplemented reaction serves as a control. The difference in dTMP incorporation between the two assays provides a measure of the activity of the ligase. The method is simple, rapid, and sensitive and can be used for the comparison of ligase levels in crude cell extracts or for monitoring ligase activity in the course of the purification of the enzyme.