The Bacillus subtilis dnaF (polC) gene that codes for the alpha subunit of the 
DNA polymerase III holoenzyme has been sequenced. It consists of 4005 base pairs 
coding for 1335 amino acids (from the start to the stop codon), giving a 
molecular weight of 151,273. A mutation (azp-12) that confers resistance to the 
antimicrobial drug 6-(p-hydroxyphenylazo)-uracil is due to a single base change 
at nucleotide 3523, from TCA to GCA, resulting in a change of the 1175th amino 
acid, serine, to alanine. It is in the active site and located at the C-terminal 
part of the enzyme. The amino acid composition in an N-terminal domain has 26% 
homology to the epsilon subunit coded by the dnaQ gene of Escherichia coli, 
which is a 3'----5' proofreading exonuclease, supporting an earlier observation 
that this function is an integral part of the polymerase molecule in B. 
subtilis.