Cleavage stimulatory factor

Bell SA, Hunt AG (2010) The Arabidopsis ortholog of the 77 kDa subimit of the cleavage stimulatory factor (AtCstF-77) involved in mRNA polyadenylation is an RNA-binding protein. FEBS Lett 584(8) 1449-1454. doi 10.1016/j.febslet.2010.03.007... 

There are, however, minor differences on the enzymes surfaces caused by amino acid insertions and deletions. These differences are most likely responsible for conferring specificity toward the interaction with factors specific for Pol I, II, and III. In addition to the 12 subunits that are either identical or homologous, Pol I contains two specific subunits, A34.5 and A49, and Pol III contains a subcomplex of three specific subunits, called C82, C34, and C31, in yeast. The location of the two Pol I—specific subunits has been determined by electron microscopy and immunolabeling (Bischler et al., 2002). The Pol I subunit A49 binds to the top of the clamp, and subunit A34.5 is located near the jaws. The location of the specific C82/C34/C31 complex of Pol III can be inferred from subunit-subunit interaction studies (Ferri et al., 2000 Flores et al., 1999). These studies indicate that the specific subcomplex is located between the largest polymerase subunit and the Rpb4/7 complex counterpart C17/C25. The Cll subunit of Pol III contains a C-terminal domain that apparently corresponds structurally and functionally to domain III of TFIIS (Chedin et al., 1998 Kettenberger et al., 2003), which inserts into the polymerase pore. Thus, in Pol III, the RNA cleavage stimulatory activity is incorporated into a polymerase subunit, in contrast to Pol II, where it is provided by the additional factor TFIIS. 

Another possibility for the stimulation of the conversion of cholesterol at a fixed substrate concentration is to stimulate the cholesterol side-chain cleavage enzyme activity. Calcium has been shown to do this but very high levels are required [59]. Other factors have been shown to have similar effects but most of the claims made in the past have not been confirmed. This applies to the rate limiting production of NADPH, the effects of specific cytosolic fractions on isolated mitochondria [60] and the stimulatory actions of specific phospholipids [61,62]. 

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