The rulB gene of plasmid pWW0 is a hotspot for the site‐specific insertion of integron‐like elements found in the chromosomes of environmental Pseudomonas fluorescens group bacteria

The rulAB operon of Pseudomonas spp. confers fitness traits on the host and has been suggested to be a hotspot for insertion of mobile elements that carry avirulence genes. Here, for the first time, we show that rulB on plasmid pWW0 is a hotspot for the active site‐specific integration of related integron‐like elements (ILEs) found in six environmental pseudomonads (strains FH1–FH6). Integration into rulB on pWW0 occurred at position 6488 generating a 3 bp direct repeat. ILEs from FH1 and FH5 were 9403 bp in length and contained eight open reading frames (ORFs), while the ILE from FH4 was 16 233 bp in length and contained 16 ORFs. In all three ILEs, the first 5.1 kb (containing ORFs 1–4) were structurally conserved and contained three predicted site‐specific recombinases/integrases and a tetR homologue. Downstream of these resided ORFs of the ‘variable side’ with structural and sequence similarity to those encoding survival traits on the fitness enhancing plasmid pGRT1 (ILE_FH1 and ILE_FH5) and the NR‐II virulence region of genomic island PAGI‐5 (ILE_FH4). Collectively, these ILEs share features with the previously described type III protein secretion system effector ILEs and are considered important to host survival and transfer of fitness enhancing and (a)virulence genes between bacteria.     

Baseline and mutagen-induced sister-chromatid exchanges in cultures of human whole blood and purified fresh or frozen lymphocytes

Baseline and mutagen-induced levels of sister-chromatid exchanges were evaluated in 10 normal individuals. Cultures with whole blood or purified lymphocytes, either freshly isolated or after 1 or 6 months of cryopreservation, were analyzed to determine whether frozen lymphocytes are suitable for SCE studies. Whole blood and freshly isolated lymphocytes were cultured from samples taken at the beginning of the study (Time 0) and 6 months later (Time 6). Cryopreserved lymphocytes were recovered after 1 month (Time 1) and 6 months (Time 6) of cryopreservation and then challenged with mutagens in culture. The mutagens used were mitomycin C, 4-nitroquinoline-1-oxide, and N-methyl-N'-nitro-N-nitrosoguanidine. Purified lymphocytes had consistently and significantly higher baseline SCE frequencies than cells from whole blood cultures and were more sensitive to N-methyl-N'-nitro-N-nitrosoguanidine and 4-nitroquinoline-1-oxide. The response to mitomycin C was similar in all culture types. There was, overall, no consistent effect of freezing on baseline or induced sister-chromatid exchange frequencies in the purified lymphocytes. This suggests that purification and cryopreservation of human lymphocytes does not alter the baseline or mutagen-induced sister-chromatid exchange response and in certain epidemiological, occupational and monitoring situations may have logistical and technical advantages over the use of fresh whole blood.     

Immunohistochemical localisation of cyclooxygenase in the human uterus

The distribution in the human uterus of the enzyme cyclooxygenase, involved in prostaglandin synthesis, was studied using the peroxidase-antiperoxidase immunohistochemical technique. Specific staining was observed only during the luteal phase of the menstrual cycle. It was found that cyclooxygenase was localised in the surface and glandular epithelium of the endometrium but could not be demonstrated in the endometrial stroma, myometrium or blood vessels. The location of specific staining for cyclooxygenase and its variation during the menstrual cycle was the same regardless of the amount of menstrual blood loss. Tissue samples obtained from early pregnant and post-menopausal patients failed to exhibit any specific staining.