Disease relevance of RPO26

• In Escherichia coli, overproduction of omega suppresses the assembly defect caused by substitution of residue 1362 of the largest subunit of RNAP, beta'. In yeast, overproduction of RPB6 suppresses the assembly defect caused by the equivalent substitution in the largest subunit of RNAP II, RPB1 [1].

High impact information on RPO26

• RPB5 encodes a 25-kD protein, RPB6, an 18-kD protein, and RPB8, a 16-kD protein [2].
• High-resolution structural analysis of the omega-beta' interface in bacterial RNAP, and comparison with the RPB6-RPB1 interface in yeast RNAP II, confirms the structural relationship and suggests a "latching" mechanism for the role of omega and RPB6 in promoting RNAP assembly [1].
• Analysis of DNA upstream of the RPB6 gene revealed an open reading frame that predicts a protein, designated PZF1, with nine C2H2 zinc fingers [3].
• The association of Rpb4/Rpb7 with Rpb6 suggests that analogous subunits of each RNA polymerase impart class-specific functions through a conserved core subunit [4].
• Loss of the Rpb4/Rpb7 subcomplex in a mutant form of the Rpb6 subunit shared by RNA polymerases I, II, and III [4].

Biological context of RPO26

• Quantitation of the amount of RPO26 mRNA showed that mutations in the Abf1p binding site reduce the expression of RPO26 by approximately 60% [5].
• In the rpo21-4 mutant, these pleiotropic phenotypes can be attributed to a defective interaction between the largest subunit and the RPO26 subunit of RNA polymerase II [6].
• Mutations in an Abf1p binding site in the promoter of yeast RPO26 shift the transcription start sites and reduce the level of RPO26 mRNA [5].
• We found that increased expression of wild-type RPO26, a single-copy, essential gene encoding a 155-amino-acid subunit common to RNAPI, RNAPII, and RNAPIII, suppressed the rpo21-4 temperature-sensitive mutation [7].
• Increasing the gene dosage of another common subunit, Rpb6p, suppresses this phenotype [8].

Anatomical context of RPO26

• Interestingly, the yeast RPB6 and TFIIIA coding sequences are divergently transcribed and are separated by only 233 base pairs, providing the potential for coregulated expression of components of RNA polymerases and the 5S rRNA component of ribosomes [3].
• We isolated the cDNA encoding the homolog of the Saccharomyces cerevisiae nuclear RNA polymerase common subunit RPB6 from hamster CHO cells [9].

Physical interactions of RPO26

• Mutations that affect Abf1p binding also result in a shift of the RPO26 transcriptional start sites to positions further upstream than normal [5].

Other interactions of RPO26

• In the presence of the wild-type allele of RPO21 these rpo26 promoter mutations confer a cold-sensitive growth defect [5].
• A binding site for the transcription factor Abf1p was identified as an important promoter element of the gene that encodes Rpo26, a subunit common to all three yeast nuclear RNA polymerases (RNAP) [5].
• Later, other groups isolated the genes for Rpb6 and Rpb12 and cDNA for Rpb10 [10].
• Hence, Rpb6p and Rpb8p functionally interact in vivo [8].
• Immunoprecipitation from 32P-labeled cell extracts revealed that three of the subunits, RPB1, RPB2, and RPB6, are phosphorylated in vivo [11].

Analytical, diagnostic and therapeutic context of RPO26

• Electrophoretic mobility-shift assays using purified Abf1p demonstrated that Abf1p binds to the RPO26 promoter and that the promoter mutations abolish this binding in vitro [5].
• ABC23 was found to be required for the formation of the first phosphodiester bond, but it was not involved in DNA binding by RNA Pol I, as shown by gel retardation and surface plasmon resonance experiments, and did not recycle during transcription [12].
• Moreover, a heterospecific complementation test showed that rpb6 from Sz. pombe fully complements a complete deletion of its S. cerevisiae homologue [13].

References