The gene encoding the psi subunit of DNA polymerase III holoenzyme, holD, was identified and isolated by an approach in which peptide sequence data were used to obtain a DNA hybridization probe. The gene, which maps to 99.3 centisomes, was sequenced and found to be identical to a previously uncharacterized open reading frame that overlaps the 5' end of rimI by 29 bases, contains 411 bp, and is predicted to encode a protein of 15,174 Da. When expressed in a plasmid that also expressed holC, holD directed expression of the psi subunit to about 3% of total soluble protein.
