Search PubMed⌕ Search

Biomedical subjects

K Jyssum

Publications and source records attributed to K Jyssum.

45 records · Page 3Linked to original sources
PubMed1968

Mutator factor in Neisseria meningitidis associated with increased sensitivity to ultraviolet light and defective transformation.

A variant of Neisseria meningitidis was found to carry a mutator factor which endowed the bacteria with generalized genetic instability. The reversion frequencies of several biochemical mutants were increased up to 1,000-fold when the factor was introduced. The factor is not unidirectional in preference, since the mutator induced mutants generally reverted with increased frequency in its presence. There could be found no indication of insufficient synthesis of nucleic acid precursors. Attempts to demonstrate an unusual, mutagenic base incorporated in deoxyribonucleic acid (DNA) were negative. Strains carrying the mutator factor had significantly increased sensitivity to ultraviolet light. A mutation to a more ultraviolet-resistant type coincided with a disappearance of the mutator property. The presence of the mutator factor in a competent strain resulted in a reduction of the transformation frequency to between 0.5 and 5% of that in the parental strain. A mutation to the more ultraviolet-resistant type resulted in simultaneous loss of the mutator property and reestablishment of a normal transformation efficiency. It has been suggested that this mutator factor may represent a defect in the DNA repair mechanism, which is also of importance for genetic recombination. The mutator factor showed cotransformation with the locus for streptomycin resistance, but a true linkage could not be proved.

DNA, Bacterial↗
PubMed1965

Polarity of chromosome replication in Neisseria meningitidis.

Jyssum, Kaare (University of Oslo, Oslo, Norway). Polarity of chromosome replication in Neisseria meningitidis. J. Bacteriol. 90:1182-1187. 1965.-Relative frequencies of various genetic markers in the deoxyribonucleic acid of Neisseria meningitidis in exponential- and stationary-growth phases were compared by use of a transformation system. On the basis of an analysis of eight genetic markers, including a competence factor, it is assumed that a polarity exists in the chromosome replication. A genetic map has been constructed according to the model of Yoshikawa and Sueoka. Chromosome replication has been compared in genetically competent and genetically incompetent strains. The change from genetic competence to genetic incompetence seems to result in a change in the replication of the chromosome. The results are discussed in relation to findings from other transformation systems, particularly that of Bacillus subtilis.

Amino Acids↗
PubMed1965

Variation in density and transformation potential in deoxyribonucleic acid from Neisseria meningitidis.

Jyssum, Kaare (University of Oslo, Oslo, Norway), and Sidsel Jyssum. Variation in density and transformation potential in deoxyribonucleic acid from Neisseria meningitidis. J. Bacteriol. 90:1513-1519. 1965.-Three variants of Neisseria meningitidis have been examined with regard to competence. One is the genetically competent M1-12 his(-)cp(+), the second is the genetically incompetent M1-12 his(-)cp(-) which does not revert to competence, and the third is the incompetent mutant M1-18 his(-)gly(-)(cp) which reverts to competence. An examination of the relation between the deoxyribonucleic acid (DNA) and protein contents indicates the existence of more DNA in strain M1-12 his(-)cp(+) than in strain M1-12 his(-)cp(-). DNA prepared from the three strains was examined by density gradient centrifugation. The distribution of DNA in the gradients was unimodal. No significant differences could be observed between the distribution curves obtained from the three test strains. When the distribution in the gradients of transformation potential corresponding to five biochemical markers was measured, a pronounced difference was found among the three test strains. The distribution of the markers in the gradient from strain M1-12 his(-)cp(-) was unimodal. In the DNA from strain M1-18 his(-)gly(-)(cp), all the markers examined showed bipartite distribution curves with low relative specific transforming activity, corresponding to an area near the middle of the DNA distribution. The strain M1-12 his(-)cp(+) showed a similar bipartite distribution of four biochemical markers, whereas the marker pro had a very high relative specific transforming activity in the area where the other markers tested had a reduced activity. The nature of the DNA with reduced transformation potential which seems to be present in strains M1-12 his(-)cp(+) and M1-18 his(-)gly(-)(cp) is discussed in relation to previous observations. The possibility has been presented that the cp factor in N. meningitidis may be a true episome.

Amino Acids↗