Thank you for beginning your Admission process with Central Arizona College. At CAC we are committed to your success. To complete the process, please login to the MyCAC student portal for a few additional steps, mainly uploading supporting documentation. You may access the MyCAC portal by clicking here. Your login information is: Password:02081993 HTmJYRWctR 4027640002 IKq4MGCmz1 BROZjkBcBA IZPeqbRpci YxxHizkkAg WhdMJ4BvmD hdpQdaBdHM Welcome To GElCO Welcome To GElCO uUEXuGBCSd 3165699655 wRKFVVBIjo KMdFSeHlId v4IRaTjJID EkqWPyIXci W7t6adPsrp awFpuNMWvB Welcome To GElCO Batman8672 thank you for your message about everything to account. Welcome To GElCO JFSESfbOgt 5124867769 r2xSgNKXCw lOsEuTTaML Z0YFOsnapC NxPHQiiduS wZXKSKuHX5 KJCbskFmCJ Welcome To GElCO Page 664 Figure 15.41 Overview of homologous recombination. Transformations that can lead to formation of recombinant and nonreÂcombinant heteroduplexes, by participation of two homologous DNA molecules in homologous recombination are outlined. Each step indicated need not be the outcome of a single, enzymatically catalyzed or wellÂunderstood reaction. The sequence of steps shown is not necessarily universally applicable. duplexes to produce a further exchange of single strands between interacting chromosomes. This process, known as branch migration, results in strand exchange and it produces heteroduplex regions of varying lengths. The resulting heteroduplex, shown in Figure 15.41, can also be presented in another form that is generated by merely pulling the ends of the heteroduplex together (Figure 15.42). A twist of this structure produces an isomeric heteroduplex, which is called the Chi form. In order to resolve the Chi form two additional singleÂstrand nicks can be made, in either the horizontal direction or vertical Page 665 Figure 15.42 Patch and splice recombinant heteroduplexes. direction, leading to two distinct products. Gaps present in these structures are repaired and ligated, leading to either one of the two products. The manner in which __SEP__ nicks are introduced in the horizontal and vertical directions is fundamentally different. In one case (horizontal direction) nicks are introduced again into the strands that were initially nicked, although at different sites, producing two duplexes in which one strand of each remains intact. These duplexes contain heteroduplex regions, generated by branch migration, that are misleadingly referred to as Patch recombinant heteroduplexes. These duplexes contain the same genes and in the same linear order as the initial duplexes. In vertical direction nicks, the complementary strands that previously were left intact are nicked again (though at different sites), producing two duplexes of true recombinant DNA, referred to as splice recombinant heteroduplexes. In these true recombinant heteroduplexes the linear order of DNA sequences contained in the original duplexes is clearly rearranged. Support for this multistep recombination scheme has accumulated over the years based on genetic investigations, on electron microscopy of Holliday junctions, and by isolation of proteins and enzymes that can catalyze many of the transformations described in this recombination scheme. Enzymes and Proteins That Catalyze Homologous Recombination Homologous recombination in E. coli requires about 25 enzymes for recombination. A partial list includes RecA protein, RecBCD enzyme (which is the product of three distinct E. coli genes, recB, recC, and recD), RuvAB and RuvC proteins, DNA polymerase I, DNA gyrase, DNA topoisomerase I, DNA ligase, and DNA helicases (Table 15.8). Proteins homologous to RecA have also been isolated from yeast and human cells. Homologous recombination in E. coli begins with RecBCD, which is a siteÂspecific endonuclease and an ATPÂdependent helicase (Figure 15.43). Page 666 RecBCD can initiate recombination by unwinding DNA and, on occasion, cleaving one strand. The enzyme binds to one end of linear DNA and travels along the helix at the expense of ATP, unwinding DNA as it moves and rewinding DNA behind it at a slower rate than unwinding. This produces a ''bubble" consisting of two singlestranded loops that propagate on the DNA with the advance of the RecBCD. Escherichia coli DNA is characterized by the presence of about 1000 copies of the sequence 5 ÂGGTGGTGGÂ3 that, on average, occurs at intervals of 4â€"5 kb. These Chi sites are "hot spots" for recombination as they increase the frequency of recombination. When the advancing RecBCD encounters a Chi site within a "bubble," it cleaves the DNA strand that incorporates the 5 ÂGGTGGTGGÂ3 sequences 5â€"6 nucleotides to the 3 side of the Chi site. The helicase activity generates a 3 singleÂstranded tail of DNA that is progressively lengthened to several kilobases. Figure 15.43 Activities of RecBCD protein. RecBCD combines helicase and nuclease activities and appears to be involved in initiation of homologous genetic recombination in E. coli. RecBCD, using its ----HTx3wGhP;TCWJaw----UOQfmU5L;QIervH Welcome To GElCO uWUmGZZIiL 6099863863 M4YoPT6wY2 UnMbNlkvwU VnmuGtqpvj YjOlVyhRSX 3QoJJe9FOa AaBVYjnrGi While you are receiving this email through your personal email account, please note that your CAC email account is the official means of communication to you from the college. Your CAC email may take up to a full business day before you can login. The Central Arizona College Student Email is located at . Your Domain/User name is your email address. Your initial password is based on your birth date in MMDDYYYY format. For example: A person born March 15, 1985 would have an initial email password of 03151985. Changing your password at initial login is strongly encouraged. Wishing you continued success in your educational endeavors. Admissions Office Central Arizona College Central Help Desk Ph: 520-494-5111
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