Termination signals, detecting

It detects termination signals that specify where a transcript ends. 

Melittin a linear, toxic (hemolytic) polypeptide amide, and the chief component of bee venom (about 50 % of dried venom, and at least in 50-fold molar excess over other venom constituents). The primary product of M. biosynthesis is prepromelittin, consisting of 70 amino acid residues Removal of the N-terminal signal sequence of 21 residues (see Signal hypothesis) leaves promelittin. The protease required for removal of the signal sequence is present in many animal cells and is not species-specific, e. g. promelittin and not prepromelittin is the first detectable product when melittin mRNA is injected into oocytes of Xenopus laevis. 

Chemical reactions consist of repeated cycles in which fluorescently labeled nucleotides are added, the reaction is terminated by a virtual terminator nucleotide, the excess unincorporated nucleotides are washed out, the fluorescent signals on the template are recorded, and the fluorescent label is cleaved from the recorded strand (Figure 90.5). Each reaction adds one of the four nucleotides (A, C, G, and T) and the template position is mapped to the signal detected on the flow cell. In this way, the exact sequence of the template strand is recorded after each cycle, including the total length in nucleotides per synthesized molecule. The overall technical performance of the Hehscope is presented in Table 90.1. 

NMR methods can be applied to give quantitative determination of initiator-derived and other end groups and provide a wealth of information on the polymerization process. They provide a chemical probe of the detailed initiation mechanism and a greater understanding of polymer properties. The main advantage of NMR methods over alternative techniques for initiator residue detection is that NMR signals (in particular nC NMR) are extremely sensitive to the structural environment of the initiator residue. This means that functionality formed by tail addition, head addition, transfer to initiator or primary radical termination, and various initiator-derived byproducts can be distinguished. 

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