Table 4.

Yeast SRB/mediator subunitsa

FactorMass (kDa)Gene(s)EssentialMetazoan homologsReference(s)
Srb223 SRB2 No 252, 260, 261, 483
Srb478 SRB4 Yes 252, 261, 483, 484
Srb534 SRB5 No 252, 261, 483
Srb614 SRB6 Yes 252, 261, 483, 484
Srb716 SRB7 YesYes 194, 283
Srb8167 SRB8, SSN5,ARE2 No 194, 283
Srb9160 SRB9, SSN2,UME2 No 194, 283
Srb1063 SRB10, SSN3, UME5,ARE1 No 265, 285, 461, 516
Srb1136 SRB11, SSN8,UME3 No 98, 265, 285
Gal1138 GAL11, SPT13, SDS4,RAR3 No 130, 252, 261
Sin4111 SIN4, SSN4,TSF3 No 72, 230, 282
Rgr1123 RGR1 YesYes 230, 282
Rox3b 25 ROX3,SSN7 Yes 170, 396
Med164 MED1 NoCited in 330
Med248 MED2 No 330
Med3, Pgd1, Hrs147 PGD1,HRS1 No 330
Med432 MED4 Yes 330
Med633 MED6,MTR32 YesYes 278
Med732 MED7 Yes 330
Med825 MED8 Yes 330
  • 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.