Cleavage factor

JCore Sequence partially homologous in all RNA polymerases. Common shared by all eukaryotic RNA polymerases, Rpb4/7 Rpb4/7 heterodimer and its structural counterparts. Unclear It is unclear if A12.2 and Cll are true Rpb9 homologs. It appears that the C-terminal domain of the Pol II subunit Cll is functionally and structurally homologous to the Pol II transcript cleavage factor TFIIS. 

Thus, the original restriction appears to result solely from the absenee of GV components within the cytoplasm. In addition, since the donor GV material in these experiments was taken solely from nonstimu-lated oocytes, the cleavage factor appears to be a storage product i.e., it is not synthesized within the GV in response to the hormones which induce maturation. 

These studies have led to the conclusion that the factor responsible for inducing DNA synthesis, unlike the cleavage factor, is not present within the GV prior to its dissolution, but is perhaps synthesized at this time in response to hormone stimulation (Gurdon, 1967 Gurdon and Woodland, 1968). The additional studies on injected, purified DNA have suggested that the inability of oocyte cytoplasm (prior to GV dissolution) to support DNA synthesis is either because of the absence of cytoplasmic DNA polymerase or the presence of an inhibitor of DNA polymerase (Gurdon and Speight, 1969). 

Ryan K (2007) Pre-mRNA 3 cleavage is reversibly inhibited in vitro by cleavage factor dephosphorylation. RNA Biol 4( 1 ) 26-33... 

Other examples illustrating the effect of substituent distribution on properties include (/) enzymatic stabiUty of hydroxyethjlceUulose (16,17) (2) salt compatibihty of carboxymethylceUulose (18,19) and (J) thermal gelation properties of methylceUulose (20). The enzymatic stabUity of hydroxyethylceUulose is an example where the actual position of the substituents within the anhydroglucose units is considered important. Increasing substitution at the C2 position promotes better resistance toward enzymatic cleavage of the polymer chain. Positional distribution is also a factor in the other two examples. 

Discrimination between exposed and unexposed areas in this process requires the selection of thia zolidine compounds that do not readily undergo alkaline hydrolysis in the absence of silver ions. In a study of model compounds, the rates of hydrolysis of model /V-methyl thia zolidine and A/-octadecyl thiazolidine compounds were compared (47). An alkaline hydrolysis half-life of 33 min was reported for the /V-methyl compound, a half-life of 5525 min (3.8 days) was reported for the corresponding V/-octadecyl compound. Other factors affecting the kinetics include the particular silver ligand chosen and its concentration (48). Polaroid Spectra film introduced silver-assisted thiazolidine cleavage to produce the yellow dye image (49), a system subsequentiy used in 600 Plus and Polacolor Pro 100 films. 

Alkyl groups under nonacidic conditions sterically deflect nucleophiles from C, but under acidic conditions this steric effect is to some extent offset by an electronic one the protonated oxirane opens by transition states (Scheme 40) which are even more 5Nl-like than the borderline Sn2 one of the unprotonated oxirane. Thus electronic factors favor cleavage at the more substituted carbon, which can better support a partial positive charge the steric factor is still operative, however, and even under acidic conditions the major product usually results from Cp attack. 

Factors of hardness, elasticity, toughness, and cleavage are important in determining grindabihty. Grindabihty is related to modulus of elasticity and speed of sound in the material [Dahlhoff, Chem. Ing. Tech., 39(19), 1112-1116 (1967)]. 

The triethylsilyl ether is approximately 10-100 times more stable than the TMS ether and thus shows a greater stability to many reagents. Although TMS ethers can be cleaved in the presence of TES ethers, steric factors will play an important role in determining selectivity. The TES ether can be cleaved in the presence of a /-butyldimethylsilyl ether using 2% HE in acetonitrile. In general, methods used to cleave the TBDMS ether are effective for cleavage of the TES ether. 

Benzylidene acetals have the useful property that one of the two C—O bonds can be selectively cleaved. The direction of cleavage is dependent on steric and electronic factors as well as on the nature of the cleavage reagent. 

Occasionally a free ketol rather than its acetate may be cleaved successfully in other cases cleavage does not occur. Starr and Smith " have summarized the available data including that covering the reduction of vinylogs of ketols. The experimental findings may be rationalized in several ways, but no firm conclusions seem possible. Smith has discussed some of the pertinent factors that must control the reduction of ketols. 

By changing from the simplest to larger aliphatic and cyclic ketones, structural factors may be introduced which favor alternative unimolecular primary photoprocesses or provide pathways to products not available to the simple model compound. In addition, both the increase in molecular size and irradiation in solution facilitate rapid vibrational relaxation of the electronically excited reactant as well as the primary products to thermally equilibrated species. In this way the course of primary and secondary reactions will also become increasingly structure-selective. In a,a -unsym-metrically substituted ketones, the more substituted bond undergoes a-cleavage preferentially. 

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