Loss of the Rpb4/Rpb7 subcomplex in a mutant form of the Rpb6 subunit shared by RNA polymerases I, II, and III.
We have identified a conditional mutation in the shared Rpb6 subunit, assembled in RNA polymerases I, II, and III, that illuminated a new role that is independent of its assembly function. RNA polymerase II and III activities were significantly reduced in mutant cells before and after the shift to nonpermissive temperature. In contrast, RNA polymerase I was marginally affected. Although the Rpb6 mutant strain contained two mutations (P75S and Q100R), the majority of growth and transcription defects originated from substitution of an amino acid nearly identical in all eukaryotic counterparts as well as bacterial omega subunits (Q100R). Purification of mutant RNA polymerase II revealed that two subunits, Rpb4 and Rpb7, are selectively lost in mutant cells. Rpb4 and Rpb7 are present at substoichiometric levels, form a dissociable subcomplex, are required for RNA polymerase II activity at high temperatures, and have been implicated in the regulation of enzyme activity. Interaction experiments support a direct association between the Rpb6 and Rpb4 subunits, indicating that Rpb6 is one point of contact between the Rpb4/Rpb7 subcomplex and RNA polymerase II. The association of Rpb4/Rpb7 with Rpb6 suggests that analogous subunits of each RNA polymerase impart class-specific functions through a conserved core subunit.
Tan
Qian
Q
Department of Molecular Genetics, Microbiology and Immunology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854-5635, USA.
Prysak
Meredith H
MH
Woychik
Nancy A
NA
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D021122:Protein Subunits; D012318:RNA Polymerase I / Q000378:metabolism; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D012320:RNA Polymerase III / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D005656:Fungal Proteins; D046911:Macromolecular Substances; D021122:Protein Subunits; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D012319:RNA Polymerase II; C423309:RPB4 protein, S cerevisiae; C470553:RPB7 protein, S cerevisiae; C485634:RPO26 protein, S cerevisiae; D012321:DNA-Directed RNA Polymerases; D012318:RNA Polymerase I; D012320:RNA Polymerase III