RNA elongation

Highly potent bacterial toxins such as ricin and diphtheria can completely inhibit cellular protein synthesis at very low levels [26]. The bacterial toxin exerts cytotoxicity through enzymatic inactivation of factors essential for protein synthesis (e.g., riboso-mal RNA, elongation factor 2 or EF2). Inactivation of these proteins, which are... 

Now, as the DNA unravels over its short genome distance (catalyzed by helicase), RNA polymerase, using the DNA template strand, transcribes the single DNA strand in the 3 5 direction with the RNA elongation taking place in the 5 3 ... 

Termination positions are defined by the thermodynamic stability of the polymerase complex, whereas the efficiencies of termination are determined by a kinetic competition between RNA elongation and release at each position (94). The termination efficiency is affected mostly by the strength of the stem—loop, the presence of the U-tract, and also by the concentration of NTP substrates. The efficiency of transcription termination also depends on other factors such as the size and shape of the hairpin, not just its stability, most likely involving interactions with the polymerase. Different RNA hairpins exert varying effects on transcription termination, while a cruciform structure may have no or some attenuating effect on transcription. Furthermore, certain changes in the stem sequence designed to maintain or raise the stability of the stem (AG = —18 kcal/mol) lead to a decrease... 

Adding nucleotides to the 3 oxygen of an existing structure is called elongation and leads ultimately to a polynucleotide The most important polynucleotides are ribonu cleic acid (RNA) and deoxyribonucleic acid (DNA) As we shall see m later sections the polynucleotide chains of DNA and some RNAs are quite long and contain hundreds of thousands of bases... 

The signal recognition particle (SRP) is a cytosolic ribonucleoprotein complex which binds to signal sequences of nascent membrane and secretory proteins emerging from ribosomes. The SRP consists of a 7S RNA and at least six polypeptide subunits (relative molecular masses 9, 14, 19, 54, 68, and 72 kD). It induces an elongation arrest until the nascent chain/ ribosome/SRP complex reaches the translocon at the endoplasmic reticulum (ER) membrane. 

Other steps of RNA synthesis such as elongation or termination also control the abundance of proteins. These are less well understood than the initiation of transcription described here. 

Ping YH, Chu CY, Gao H, Jacque JM, Stevenson M, Rana TM (2004) Modulating HlV-1 replication by RNA interference directed against human transcription elongation factor SPT5, Retro-virology 1 46... 

The general topology of rubredoxins is also observed in the general zinc-ribbon motif in RNA polymerases or in transcription factors (59). The first published zinc-ribbon structure was that of the nucleic-acid binding domain of human transcriptional elongation factor TFIIS (PDB file ITFI) 40). These zinc binding domains and rubredoxins... 

Dias N., Senamaud-Beaueort G., Le Fo-RESTiER E., Auvin G., Helene G., Saison-Behmoaras T. E. RNA hairpin invasion and ribosome elongation arrest by mixed base PNA oligomer. J. Mol. Biol. 2002 320 489-501. 

The processes of DNA and RNA synthesis are similar in that they involve (1) the general steps of initiation, elongation, and termination with y to 3 polarity (2) large, multicomponent initiation complexes and (3) adherence to Watson-Crick base-pairing rules. These processes differ in several important ways, including the... 

Template binding RNA polymerase (RNAP) binds to DNA and locates a promoter (P) melts the two DNA strands to form a preinitiation complex (PIQ. (2) Chain initiation RNAP holoenzyme (core + one of multiple sigma factors) catalyzes the coupling of the first base (usually ATP or GTP) to a second ribonucleoside triphosphate to form a dinucleotide. (3) Chain elongation Successive residues are added to the 3 -OH terminus of the nascent RNA molecule. (4) Chain termination and release The completed RNA chain and RNAP are released from the template. The RNAP holoenzyme re-forms, finds a promoter, and the cycle is repeated. 

RNA SYNTHESIS IS A CYCLICAL PROCESS INVOLVES INITIATION, ELONGATION,... 

Initiatioii of formation of the RNA molecule at its 5 end then follows, while elongation of the RNA mole-... 

---