Walter Vielmetter

Complete maps of IS1, IS2, IS3, IS4, IS5, IS30 and IS150 locations in Escherichia coli K12

SummaryIn this paper complete distribution maps are presented of the seven IS elements 1, 2, 3, 4, 5, 30 and 150. These maps were obtained during the construction of an almost complete restriction map of the Escherichia coli genome of K12 strain BHB2600. The positions of IS elements were correlated to this map. The distribution of integration sites of all IS types is nonrandom. Besides a large gap from 79 min to 96 min, there is a pronounced IS cluster at 6 min and another at 97 min, map locations that have low gene incidences on the classical map. One cluster coincides with a region of IS induced rearrangements. The IS distribution pattern was compared to patterns of strains W3110 and HB101.

Activation of a system for the joining of nonhomologous DNA ends during Xenopus egg maturation.

Mature Xenopus laevis eggs provide an elementary reaction system of illegitimate recombination which efficiently joins nonhomologous DNA ends (P. Pfeiffer and W. Vielmetter, Nucleic Acids Res. 16:907-924, 1988). Here we show that stage VI oocytes, known to express a system for homologous recombination (D. Carroll, Proc. Natl. Acad. Sci. USA 80:6902-6906, 1983), are completely devoid of this joining system. Nonhomologous DNA end-to-end joining, however, attains full activity only at an extremely late stage of egg maturation. Cycloheximide inhibition patterns indicate that nonhomologous joining activity is regulated at the G2 restriction point of the cell cycle. Implications of homologous and nonhomologous recombination activities during egg maturation are discussed.

COMPLETION OF THE IS MAP IN E. COLI : IS186 POSITIONS ON THE E. COLI K12 CHROMOSOME

SummaryInsertion sites of the transposable element IS186 were physically mapped in the genome of E. coli K12 strain BHB2600. This strain maintains four IS186 copies of which three, assigned to 0.3, 14.1 and 51.8 map min., share common map positions with the three IS186 copies in strains W3110 and HB101. The fourth, unique IS copy in BHB2600 maps at 49.3 min. The IS186 data complete the BHB2600 map for all chromosomal sites of known K12-associated IS types.

A novel nuclease activity from Xenopus laevis releases short oligomers from 5′‐ends of double‐and single‐stranded DNA

Background: Double‐strand breaks in chromosomal DNA of eucaryotic cells are assumed to be repaired by mechanisms of illegitimate recombination capable of direct rejoining of the broken ends. Cell‐free extracts of Xenopus laevis eggs efficiently perform these end joining reactions with any pair of noncomplementary DNA termini whose single‐stranded 5′‐ or 3′‐overhangs do not exceed a length of ≈ 10 nt.

A recA-dependent mutator of Escherichia coli K12: Method of isolation and initial characterization

A number of mutator strains of E. coli were isolated using histochemical techniques which allow the identification of a single mutator colony on agar plates with as many as 2000 colonies. Several mutators isolated in this way were found by P1-mediated transduction to map to the proA--proB region of the E. coli chromosome. The map position of these mutators is very close to that of the conditional mutator, mutD. However, in contrast to mutD, one of these newly isolated mutators was suppressed in a thermosensitive recA strain at 43 degrees C, but not at 30 degrees C. This mutator mutation has been named mut-8. Besides being dependent upon recA, mut-8 is also dependent upon growth in enriched medium for the expression of its mutator activity. The mutator activity of mut-8 was found to be recessive to the wild-type allele.