body leg fool

Co-activators Abound: Mediator, CBP/p300, OCA, and Others

Of course, the TAFs and TFIID turned out to be merely the tip of the iceberg when it comes to co-activators. Using a combination of biochemistry and genetics a large number of co-factors, mediators, and co-regulators soon emerged. Among them were the yeast mediator and a series of mammalian coactivator complexes isolated in multiple labs and named CRISP, TRAP, DRIP, etc (Boyer et al., 1999; Fondell et al., 1996; Kim et al., 1994b; Naar et al., 1998; Rachez et al., 1999; Ryu et al., 1999; Sun et al., 1998). Upon further purification and identification of the subunits, all of these complexes were found to be related and are now generally referred to as the Mediator. As a co-activator complex, the Mediator is not required for basal transcription in vitro and has not been found to bind DNA directly. Instead, it is thought to be recruited to promoters via interaction with promoter bound transcriptional activators where it facilitates the binding of RNA polymerase II. This class of co-activators also is able to directly bind to the CTD of RNA pol II and thus further integrate complex mechanisms of transcriptional control (Kim et al., 1994a). A large and diverse group of activators have been found to bind the mediator complex, and EM studies revealed that the binding of activators can grossly alter the conformation of the co-activator complexes (Fig. 1.6) (Taatjes et al., 2002; Taatjes et al, 2004).

CRSP can be Converted lo Alternate Conformations SREBP VP16 CRSP-SREBP —■^ CRSP ^ - CRSP-VP 16

0 0

Post a comment