DNA-Protein Complex in Circular DNA from Bacillus Bacteriophage GA-1

DNA prepared from bacteriophage GA-1 contains circular DNA molecules, which are converted to linear molecules by treatment with trypsin

Effect of concentration on the subsequent fate of plasmid DNA in human fibroblasts

The physical fate of plasmid DNA after entry into human fibroblasts was studied using Southern hybridisation and electron microscopy. Exposure of the cells (5x105 per well) to pC194 DNA-CaPi, containing 50 μg plasmid DNA, resulted in the occasional formation of interlocked molecules. Exposure to a co-precipitate containing 100 μg pC194 plasmid DNA per well resulted in an increase of interlocked molecules by a factor of 10–20 relative to the number of monomers. In addition, new classes of molecules were observed. After prolonged incubation of the cells exposed to the higher DNA concentration, the plasmid DNA was partly contained in structures with a very low electrophoretic mobility. Upon restriction endonuclease digestion of the re-extracted DNA, a pattern of bands was observed, suggesting the involvement of illegitimate recombination between non-random plasmid DNA sequences in the formation of the new classes of molecules

Identification and organization of carbon dioxide fixation genes in Xanthobacter flavus H4-14

The genes encoding the large (cfxL) and small (cfxS) subunits of ribulose-1,5-bisphosphate carboxylase (RuBisC/O) from Xanthobacter flavus H4-14 were identified and characterized. The RuBisC/O genes are separated by 11 bp and cotranscribed in Escherichia coli from the lac promoter in the order cfxLS. Primer extension and R-loop experiments with RNA isolated from autotrophically grown X. flavus H4-14 showed that transcription of cfxL and cfxS initiated 22 bp upstream from cfxL and resulted in a mRNA of at least 2.3 kb. DNA sequence analysis identified the start of an open reading frame transcribed divergently from cfxL, and displaying significant similarities with genes belonging to the lysR family of transcriptional activators. Downstream from cfxS an additional open reading frame was identified with unknown function. Expression studies showed that the genes encoding fructosebisphosphatase (cfxF) and phosphoribulokinase (cfxP) are located downstream from cfxLS. The cfxF and cfxP genes are cotranscribed in the same direction as cfxLS in the order cfxFP.