Repair of closely opposed cyclobutyl pyrimidine dimers in UV-sensitive human diploid fibroblasts

An enzyme-sensitive site assay has been used to examine the fate of closely opposed pyrimidine dimers (bifilar enzyme-sensitive sites) in fibroblasts from individuals afflicted with various genetic disorders that confer increased cellular sensitivity to UV radiation. The disappearance of bifilar enzyme-sensitive sites was found to be normal in cells from individuals with Fanconi's anemia, Cockayne's syndrome, dyskeratosis congenita and the variant form of xeroderma pigmentosum. The rate of bifilar enzyme-sensitive site removal in XP cells assigned to complementation group C was reduced by an amount similar to that observed for the repair of isolated dimers. Our results indicate that the initiation of repair at closely opposed dimers is slow in XP-C cells but normal in all other cells examined.     

Pseudoterminalisation,terminalisation, and non-chiasmate modes of terminal association

Terminal associations occur commonly between meiotic homologues of the two smallest (S10, S11) chromosomes in the northern race of Cryptobothrus chrysophorus when they are either heterozygous or homozygous for distal supernumerary heterochromatic segments. A detailed examination of the origin and behaviour of these associations provides convincing evidence that they are non-chiasmate in character and so cannot be explained by either pseudoterminalisation or terminalisation. The same is true of the terminal associations involved in the persistent pseudomultiples that develop between non-homologues of Heteropternis obscurella when one or both of these carry distal heterochromatic segments. In both situations the C-bands involved in such terminal associations are entire and are never interrupted by non-banded material. In Cryptobothrus, similar associations can also develop between centromere regions when these are heterozygous or homozygous for proximal supernumerary heterochromatic segments.     

Mutagens in rat urine after dermal application of 1,3-diaminobenzene

The mutagenicity of urine from rats treated topically on the skin with 1,3-diaminobenzene was studied by the Salmonella/mammalian-microsome assay. Urine samples were either passed directly through micropore filters or extracts were prepared using XAD-2 resin before testing in the frameshift strain TA98. Significant mutagenic activity was found only after metabolic activation with rat-liver microsomes. The activity was higher in extracts from rats treated with a mixture of hydrogen peroxide and 1,3-diaminobenzene than from rats which were exposed to 1,3-diaminobenzene only. After fractionation of the urine by HPLC it could be demonstrated that the mutagenic activity was not due to the parent amine but related to metabolites in two of the fractions. To a lesser extent these two partially purified fractions were also mutagenic without S9 activation even though it was not possible to demonstrate this effect in unfractionated urine extracts. A third fraction containing two metabolites did not exert demonstrable mutagenic activity. The implications for the assessment of hazard to man are discussed.     

Light-temperature interactions in the control of photosynthesis in Antarctic phytoplankton

Summary During October/November 1983 photosynthetic responses of natural phytoplankton from the Scotia Sea and Bransfield strait to light and temperature were examined in incubators. Both assimilation numbers at saturating light levels and the slopes of the light-limited portions of the photosynthesis versus irradiance curves were smaller than in algae from lower latitudes. However, both parameters increased significantly with rising temperatures. Light-saturated photosynthesis on the average exhibited a Q₁₀-value of ca. 4.2 between-1.5°C and +2°C. Light-limited photosynthesis between-1.5°C and +5°C rose at a rate corresponding to a Q₁₀-value of roughly 2.6. Above +5°C, temperature enhancement of both light-saturated and light-limited photosynthetic rates was minimal or absent. Our results suggest that under extremely low temperatures light-limited photosynthetic rates become temperature-dependent due to changes in maximum quantum yields.     

Macrophages express cell surface laminin

Laminin, a non-collagenous extracellular connective tissue glycoprotein, was detected on the surface of mouse peritoneal macrophages. As determined by indirect immunofluorescence, as many as 60% of peritoneal macrophages elicited with thioglycollate expressed cell surface laminin. Only 14% of resident cells displayed detectable laminin. The expression of laminin increased with time post-injection. Concomitant with laminin expression, macrophages also displayed a receptor for the IB4 isolectin from Griffonia simplicifolia. This lectin, which binds methyl-alpha-D-galactopyranoside, may also react with the carbohydrate moeity of laminin. A small population of macrophages displayed both laminin and surface fibronectin. Unlike the difference in laminin expression between resident and thioglycollate-stimulated cells, there was no difference in cell surface fibronectin between these cell populations. Since laminin has been found to mediate cell attachment in other systems, expression of this molecule on the surface of stimulated macrophages may be important in cell-cell and cell-matrix adhesive properties of these cells.     

The key role of residue 5 in angiotensin II

The conformation–biological activity relationships in a series of angiotensin II analogs substituted in position 5 were studied. Results indicated that only analogs with β-branched residue in position 5 possess spectral and biological properties identical to that of parent angiotensin II.     

Structural investigation of the capsular polysaccharide produced by a novel Klebsiella serotype (SK1). Location of O-acetyl substituents using NMR and MS techniques

The capsular polysaccharide of Klebsiella SK1 was investigated by methylation analysis, Smith degradation, and ¹H NMR spectroscopy. The oligosaccharides (P1 and P2) obtained by bacteriophage ΦSK1 degradation of the polymer were studied by methylation analysis, and 1D- and 2D-NMR spectroscopy. The resulting data showed that the patent repeating unit is a branched pentasaccharide having a structure identical to the revised structure recently proposed for Klebsiella serotype K8 capsular polysaccharide.

The 2D-NMR data showed that one third of the glucuronic acid residues in the SK1 polymer are acetylated at O-2, O-3, or O-4. FABMS studies confirmed the presence of monoacetylated glucuronic acid residues. Thus, the relationship between the Klebsiella K8 and SK1 polymers is akin to that found for Klebsiella polysaccharides K30 and K33, which have been typed as serologically distinct yet their structures differ only in the degree of acetylation.     

IS200: a Salmonella-specific insertion sequence

A new IS element (IS200) has been identified in Salmonella. The sequence was identified as an IS element by the following criteria: its insertion caused the mutation hisD984; six copies of the sequence are present in strain LT2 of S. typhimurium; and transposition of the sequence has been observed on several occasions. IS200 is found in almost all Salmonella species examined but is absent from most other enteric bacteria. The specificity of this element for Salmonella (and the absence of IS1-IS4 from Salmonella) suggest that transfer of insertion sequences between bacterial groups may be less extensive than is commonly believed. Alternatively, the distribution may suggest that these elements play a selectively important role in bacteria.