The DNA sequence of the F plasmid origin of conjugal DNA transfer, oriT, has been determined. The origin lies in an intercistronic region which contains several inverted repeat sequences and a long AT‐rich tract. Introduction of a nick into one of the DNA strands in the oriT region precedes the initiation of conjugal DNA replication, and the position of the strand‐specific nicks acquired by a lambda oriT genome upon propagation in Flac‐carrying cells has been determined. The nicks were not uniquely positioned, rather there was a cluster of three major and up to 20 minor sites: the biological significance of this observation is not yet fully clear. Nine independent point mutations which inactivate oriT function have been sequenced and found to alter one or other of two nucleotide positions which lie 14 and 19 bp to one side of the rightmost (as drawn) major nick site. These key nucleotides may lie in a recognition sequence for the oriT endonuclease, since mutations at these sites prevent nicking at oriT .

Cells of the Escherichia coli dnaE(Ts) dnaE74 and dnaE486 mutants die after 4 h of incubation at 40°C in Luria-Bertani medium. Cell death is preceded by elongation, is inhibited by chloramphenicol, tetracycline, or rifampin, and is dependent on cell density. Cells survive at 40°C when they are incubated at a high population density or at a low density in conditioned medium, but they die when the medium is supplemented with glucose and amino acids. Deletion of recA or sulA has no effect. We isolated suppressors which survived for long periods at 40°C but did not form colonies. The suppressors protected against hydroxyurea-induced killing. Sequence and complementation analysis indicated that suppression was due to mutation in the cydA gene. The DNA content of dnaE mutants increased about eightfold in 4 h at 40°C, as did the DNA content of the suppressed strains. The amount of plasmid pBR322 in a dnaE74 strain increased about fourfold, as measured on gels, and the electrophoretic pattern appeared to be normal even though the viability of the parent cells decreased 2 logs. Transformation activity also increased. 4,6-Diamidino-2-phenylindole staining demonstrated that there were nucleoids distributed throughout the dnaE filaments formed at 40°C, indicating that there was segregation of the newly formed DNA. We concluded that the DNA synthesized was physiologically competent, particularly since the number of viable cells of the suppressed strain increased during the first few hours of incubation. These observations support the view that E. coli senses the rate of DNA synthesis and inhibits septation when the rate of DNA synthesis falls below a critical level relative to the level of RNA and protein synthesis.Cell division and DNA synthesis are coupled in all organisms, but the mechanism of the coupling is not clear, notwithstanding the sophisticated description of an operon with multiple promoters determining the production of the FtsZ and other proteins involved in cell division (12,15). In Escherichia coli, the completion of a round of DNA synthesis is usually followed by activation of the cell septation machinery, but synthesis does not trigger septation (4). DNA damage or other blocks to DNA synthesis often lead to inhibition of cell division. For example, induction of the SOS repair pathway activates the sulA gene product, inhibiting cell division (5). Some signal recognizes that the DNA has been damaged (or that synthesis has been inhibited), and as a result division is suspended. Deprivation of thymine necessarily inhibits DNA synthesis and also leads to filamentation (1). Filamentation often accompanies cell death, and there have been numerous studies attempting to elucidate the mechanism of death both as a result of thymine starvation and as a result of other pathways to filamentation.As part of an investigation of the roles of the different DNA polymerases in mutation (35), we studied the behavior of strains carrying a temperature-sensitive (Ts) mutation in the alpha subunit of the replicative DNA polymerase...

Eleven genes were mapped to the porcine genome with the aim of improving the human-porcine comparative gene map. Five of these genes were from regions of the human genome painted by porcine chromosomal probes; of these, two mapped to chromosomes not expected from the painting results. Among the six genes from human regions not painted by porcine chromosomal probes, three genes did not map where expected by the principle of parsimony. Several of the gene assignments indicate the existence of small regions of conserved synteny not detected by heterologous chromosome painting, especially in telomeric regions. We have also detected new rearrangements in gene order within the regions of correspondence between human Chromosome (HSA) 15 and porcine Chromosome (SSC) 1 as well as between HSA4 and SSC8.

The mitogen-induced gene, GEM, encodes a GTP-binding protein that belongs to a new family within the Ras superfamily. The regulated expression pattern of Gem suggests a role for this protein in cellular responses to growth stimulation. To facilitate the assessment of the possible role of GEM in heritable and spontaneous disease processes, the genomic organization of human GEM and the chromosomal localization of human and murine GEM have been determined. GEM has been localized to the long arm of human chromosome 8 (8q13-q21) between the D8S85 and CA2 loci by genetic linkage analysis using an MspI restriction fragment length polymorphism within GEM. No consistent somatic chromosomal alterations or heritable diseases are associated with this region. Mouse Gem maps to the proximal region of chromosome 4 between Mos and Cga. To gain insight into the transcriptional regulation of GEM, we have established the transcriptional initiation site of GEM in human T cells and defined a 5' upstream region sufficient for mitogen-responsive, inducible transcription.