Table 4.

Yeast SRB/mediator subunitsa

FactorMass (kDa)Gene(s)EssentialMetazoan homologsReference(s)
Srb223SRB2No252, 260, 261, 483
Srb478SRB4Yes252, 261, 483, 484
Srb534SRB5No252, 261, 483
Srb614SRB6Yes252, 261, 483, 484
Srb716SRB7YesYes194, 283
Srb8167SRB8, SSN5,ARE2No194, 283
Srb9160SRB9, SSN2,UME2No194, 283
Srb1063SRB10, SSN3, UME5,ARE1No265, 285, 461, 516
Srb1136SRB11, SSN8,UME3No98, 265, 285
Gal1138GAL11, SPT13, SDS4,RAR3No130, 252, 261
Sin4111SIN4, SSN4,TSF3No72, 230, 282
Rgr1123RGR1YesYes230, 282
Rox3b25ROX3,SSN7Yes170, 396
Med164MED1NoCited in 330
Med248MED2No330
Med3, Pgd1, Hrs147PGD1,HRS1No330
Med432MED4Yes330
Med633MED6,MTR32YesYes278
Med732MED7Yes330
Med825MED8Yes330
  • a Srb2, Srb4, Srb5, Srb6, and Srb7 are subunits of the SRB/mediator as described by both the Kornberg and Young laboratories. Srb8 to Srb11 are components of the SRB/mediator defined by Young and coworkers (194) but not by Kornberg and coworkers (330). The SWI/SNF complex has also been reported by Young and colleagues to be associated with the holoenzyme (535) but is not included in the SRB/mediator defined by Kornberg and coworkers (330). Sug1 was identified as a suppressor of a gal4 mutation (468) and proposed to be a component of SRB/mediator (252, 261, 469). More recently, Sug1 has been defined as a subunit of the 26S proteosome (402) and is no longer included as a subunit of the SRB/mediator (330).

  • b Rox3 was initially reported to be identical to Med8 (170). Subsequent analysis of Med8 revealed two distinct polypeptides, one of which is Rox3; however, the Med8 designation was retained for the other (330). Accordingly, Rox3 and Med8 now refer to distinct polypeptides that are both components of SRB/mediator.