The intragenic permissive chromatin regions are flanked by the repressive mark, H3K9me3, and the maintenance of the intragenic chromatin boundary appear to functions as a checkpoint in elongation [51].
By down-regulating Bub3 using RNAi, we showed that depletion of Bub3 abrogates the metaphase arrest induced by nocodazole, further indicating that Bub3 functions as a checkpoint protein, which is consistent with previous studies [30], [62], [63].
Rad24 RFC functions as a checkpoint protein that is crucial for DNA processing, recombination partner choice and cell survival after various stresses and the subsequent DNA repair (Aylon and Kupiec 2003; Aylon et al. 2003).
They also indicate that the capping process may function as a critical checkpoint that determines whether a pre-mRNA should be further processed.
Meanwhile DBC1 may function as a G2 M checkpoint factor, two recent studies suggested a function of DSB repair properties of DBC1, and these studies established the importance of phosphorylation at Threonine 454 residue of DBC1 by ATM/ATR following genotoxic stress (Yuan et al, 2012; Zannini et al, 2012).
The known functions of some of its members, for example AP1, the module's central location in the inferred network, and its preferential targeting by pathogens suggest that it may be an early mediator of downstream functions, possibly as a checkpoint of progression to apoptosis or inflammation.
However, gen-1 null mutants are fertile and show no change in CO recombination which suggests that gen-1 functions primarily as a checkpoint gene in C. elegans, or that other factors exist that work redundantly to gen-1 at the level of HJ resolution (Bailly et al. 2010).
15– 17 Because PD-1-deficient mice suffer from spontaneous autoimmune diseases, PD-1 is considered to function as an immune checkpoint molecule that is indispensable for immunological homeostasis.
This obvious function of ENV1 as a checkpoint in heterotrimeric G-protein signaling led to the question, whether this impact may be exerted via interference of ENV1 with the previously identified feedback regulation of gna1 and gna3.
Because of its integral function as a cell cycle checkpoint during mitosis, MAD2 is also thought to have a function in paclitaxel resistance (Sudo et al, 2004).
