E. coli chromosome

Because of the double helical nature of DNA molecules, their size can be represented in terms of the numbers of nucleotide base pairs they contain. For example, the E. coli chromosome consists of 4.64 X 10 base pairs (abbreviated bp) or 4.64 X 10 kilobase pairs (kbp). DNA is a threadlike molecule. The diameter of the DNA double helix is only 2 nm, but the length of the DNA molecule forming the E. coli chromosome is over 1.6 X 10 nm (1.6 mm). Because the long dimension of an E. coli cell is only 2000 nm (0.002 mm), its chromosome must be highly folded. Because of their long, threadlike nature, DNA molecules are easily sheared into shorter fragments during isolation procedures, and it is difficult to obtain intact chromosomes even from the simple cells of prokaryotes. 

AcrAB- TolC Tetracycline, fluoroquinolones, chloramphenicol, p-lactams except imipenem, novobiocin, erythromycin, fusidic acid, rifampicin E. coli Chromosome... 

Lycopene is a carotenoid with anticancer properties. To improve the production of lycopene by increasing the IPP flux in an engineered E. coli, the dxs gene was overexpressed and enhanced lycopene production was obtained [45]. In another example, the native promoters of DXP pathway genes in the E. coli chromosome were replaced with the strong bacteriophage T5 promoter (PTs), and the increase in isoprenoid precursors resulted in improved /3-carotene production (with a titer of 6 mg/g dry cell weight) [44]. 

There are at least two assembly domains, namely the L20 domain and the L15 domain, in the 50 S assembly map (Fig. 15). Proteins within the L20 domain are essential for the assembly but not for the function of the 50 S subunit whereas those in the L15 domain are functionally important proteins whose assembly occurs at a late state. As with the 30 S subunit, the assembly map of the 50 S subunit (Rohl and Nierhaus, 1982) not only reflects the assembly dependence but also the topographical relationship of the proteins within the ribosomal particle. This conclusion is supported by a good correspondence between the assembly map on the one hand, and results from cross-linking studies and from the sequential removal of proteins from the particle by LiCl on the other hand. There is also a correlation between the interdependence of proteins during the assembly process and the arrangement of their genes on the E. coli chromosome (Rbhl et al., 1982). 

B. J. Brewer, When polymerases collide Replication and the transcriptional organization of the E. coli chromosome. Cell 53, 679-686 (1988). 

FIGURE 25-1 Map of the E. coli chromosome. The map shows the relative positions of genes encoding many of the proteins important in DNA metabolism. The number of genes known to be involved provides a hint of the complexity of these processes. The numbers 0 to 100 inside the circular chromosome denote a genetic measurement called minutes. Each minute corresponds to -40,000 bp along the... 

The timing of replication initiation is affected by DNA methylation and interactions with the bacterial plasma membrane. The oriC DNA is methylated by the Dam methylase (Table 25-3), which methylates the Na position of adenine within the palindromic sequence (5 )GATC. (Dam is not a biochemical expletive it stands for DNA adenine methylation.) The oriC region of E. coli is highly enriched in GATC sequences—it has 11 of them in its 245 bp, whereas the average frequency of GATC in the E. coli chromosome as a whole is 1 in 256 bp. 

Termination Eventually, the two replication forks of the circular E. coli chromosome meet at a terminus region containing multiple copies of a 20 bp sequence called Ter (for terminus) (Fig. 25-17a). The Ter sequences are arranged on the chromosome to create a sort of trap that a replication fork can enter but cannot leave. The Ter sequences function as binding sites for a protein called Tus (terminus utilization substance). The Tus-Ter complex can arrest a replication fork from only one direction. Only one Tus-Ter complex functions per replication cycle—the complex first encountered by either... 

Replication of the E. coli chromosome involves many enzymes and protein factors organized in replication factories, in which template DNA is spooled through two replisomes tethered to the bacterial plasma membrane. 

Replication of the E. coli Chromosome The E. coli chromosome contains 4,639,221 bp. 

Each nucleotide pair contributes 0.34 nm to the length of the DNA molecule thus, the total length of DNA of an E. coli chromosome is 1.4 mm. This is about 700 times the length of the cell which contains it. Clearly, the molecules of DNA are highly folded, a fact that accounts for their appearance in the electron microscope as dense aggregates called nucleoids, which occupy about one-fifth of the cell volume (Fig. 1-4). 

Figure 25-1 Aromatic biosynthesis by the shikimate pathway. The symbols for several of the genes coding for the required enzymes are indicated. Their locations on the E. coli chromosome map are shown in Fig. 26-4. The aminoshikimate pathway which is initiated through 4-aminoDAHP leads to rifamycin and many other nitrogen-containing products.

The product of step o is known as isochoris-mate.55 56 Isochorismate gives rise to a variety of products including vitamin K, salicylic acid,56a the iron chelator enterobactin (Fig. 16-1), and other siderophores. These are formed in E. coli via 2,3-dihy-droxybenzoate as indicated in Fig. 25-2.57-59a The genes (ent) for the requisite enzymes are clustered at 14 min on the E. coli chromosome map (Fig. 26-4). 

The directions of transcription of certain operons are indicated by the arrows. The 1983 version of this map76 contained 1027 loci and we now know the location of all of the more than 4300 genes. (B) Physical map of the E. coli chromosome obtained by study of large 20-100 kb fragments obtained by digestion with restriction endonuclease Notl and separated by pulsed field gel... 

Although the action of the DNA polymerase I, according to Eq. 27-3, provided a straightforward way to form a complementary strand of DNA, it did not explain how double-stranded DNA could be copied. One problem is that the two strands must be separated and unwound. If unwinding and replication occured at a single replication fork in the DNA, as indicated by Caims experiment, the entire molecule would have to spin at a speed of 300 revolutions per second to permit replication of the E. coli chromosome in 20 min. It also required that some kind of a swivel, or at least a... 

A) Replication forks in the E. coli chromosome. The autoradiographic pattern was produced by a chromosome that initiated replication with [3H] thymine (5 Ci / mmol) and was subsequently labeled with [3H]thymidine (52 ci / mmol) for 6 min. 

Since the reaction doesn t require accessory protein factors and can be performed in vitro with a variety of DNA substrates, the Cre-loxP system is much used in genetic engineering.583 584 A pair of related integrase subunits known as XerC and XerD perform a similar function for the E. coli chromosome as well as for multicopy plasmids.585 586 The XerC / XerD system is... 

There are seven rRNA regions in the E. coli chromosome.2083 Each region consists of a single transcriptional unit containing a gene each for 16S, 23S, and 5S... 

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