Numerous physical and genetic approaches have identified residues in the alpha, beta, beta' and sigma subunits of Escherichia coli RNA polymerase that are involved in transcriptional processes; in contrast, relatively little data exist to demonstrate interacting regions within or between the subunits themselves. As a means of identifying regions in the beta subunit that may interact, we have sought intragenic suppressor mutations of a class of elongation-defective and termination-proficient inviable rpoB alleles that affect highly conserved residues. We obtained intragenic allele-specific suppressors of GD566 (located in conserved region D) and AV676 (located in conserved region E). With one exception, these allele-specific suppressors also map to highly conserved regions of the beta subunit. Allele specific suppression is a genetic criterion for protein-protein interaction. Moreover, the functional properties of the mutants suggests that suppression is likely to result from protein-protein interaction rather than from functional compensation. Our suppression studies provide evidence for the interaction of conserved regions B and D as well as conserved regions E and H of the beta polypeptide. We suggest that these, as well as other conserved regions of the beta polypeptide, may interact with each other to provide a framework for the function of the enzyme.