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The 8-hydroxy-2'-deoxyguanosine (8-OHdG) is a DNA base modified by reactive oxygen species (NOS). The 8-OHdG has been shown to be generated in the brain during ischemia-reperfusion. We performed the immunohistochemical study of 8-OHdG in the brains of autopsied specimens. Age had a statistically significantly negative correlation with 8-OHdG immunoreactivity in glial cells. The 8-OHdG immunoreactivity in glial cells was not increased in the surrounding border of the infarction compared with the non-ischemic areas in the same cases. There was no statistically significant difference in the disease-free areas between infarction and the age-matched control cases. This indicates that 8-OHdG immunoreactivity may not be a sensitive tool to evaluate the infarction injury in human autopsied specimens.

A temperature-sensitive mutant of Bacillus subtilis, CRK2001, defective in the initiation of DNA replication is described. When the temperature was raised, initiation of DNA replication was immediately prevented, while on-going replication continued to complete rounds of replication. Reinitiation occurred from the normal replication origin 10 to 15 minutes after cells heated to 47°C were cooled to 30°C. The reinitiation did not require protein synthesis but did require de novo RNA synthesis. The ability of the cell to reinitiate replication either at 47°C or in the presence of rifampicin returned very rapidly at 30°C. Using a rifampicin-reversible derivative of CRK2001 it could be shown that a temperature-resistant initiation potential (cell's ability for initiating replication at 47°C) was formed at 30°C just as rapidly in the presence of rifampicin as in its absence. This indicates that both reactivation of a temperature-sensitive product (Pten7) and de novo synthesis of initiation RNA are required for the reinitiation. I-RNA ‡ synthesis occurred at 47°C as well as at 30°C, but it turns over rapidly with a half-life of two minutes in the absence of the active gene product. The half-life of I-RNA in this state was appoximately the same as that of average messenger RNA. A completed initiation potential was formed at 30°C in the absence of thymine. It remained stable at 47°C but decayed slowly in the presence of rifampicin. The half-life of RNA in this stage was 12 minutes and was much longer than that of I-RNA synthesized in the absence of active gene product. A sequence of events involved in the formation of the initiation potential in this mutant was constructed based on these observations.

A specific action of sodium dodecyl sulfate (SDS) on the sex (F) factor in the integrated state of Escherichia coli K-12 Hfr H strain is reported. Growth of Hfr cells in Penassay Broth containing SDS results in the elimination of part or all of the F factor, yielding low and nonfertile variants of defective Hfr type and F + cells and also F − derivatives. Appearance of such variants was generally observed after the culture reached stationary phase. The frequencies of F − cells then increased. F − cells were usually isolated as the major population among survivors. Some defective variants of Hfr cells with an intermediate fertility between standard Hfr and F + cells had lost sensitivity toward the male-specific ribonucleic acid phage M12. Other defective Hfr variants with as much or less fertility than standard F + cells had also all lost sensitivity to phage M12. On single-colony isolation, they segregated nonfertile female H cells which, when infected with F, could restore high fertility with oriented transfer of the chromosome the same as that of the original Hfr H. Also, sensitivity to phage M12 was regained. Female H cells were characterized as those lacking fertility but still retaining a small segment of F or sfa locus at the original part of the chromosome, where newly infected F could attach. Similar results were obtained with two other Hfr strains. A possible mechanism of the specific action of SDS is discussed.

Regions of the plasmid genome essential for plasmid replication and maintenance in Escherichia coli have been identified for two antibiotic resistance Plasmids, RK2 and R6K. In both cases a small segment of the plasmid, containing an origin of replication, has been maintained as an extrachromosomal element when another essential region(s) of the plasmid that specifies a trans-acting product is present in the host cell. Nucleotide sequence analysis of the origin regions of plasmids RK2 and R6K revealed seven 22 base pair (bp) direct repeats in tandem for the R6K origin region and eight 17 bp direct repeats in clusters of three and five for RK2. A model is presented involving the interacting of the π protein, the trans-acting product of the R6K genome that is required for the initiation of R6K replication, with the 22 bp direct repeats as a necessary step in the initiation of plasmid R6K replication.