The polB gene encodes DNA polymerase II in Escherichia coli. The nucleotide sequence shows an open reading frame of 2,304 nucleotides coding for a protein of 88 kD. The protein initiation signal is preceded by a lexA box lying 2 nucleotides from the termination signal of araD, and begins with GUG 75 nucleotides after the termination of araD. The polB gene and the araD gene are transcribed in the same direction. Initiation of protein synthesis was confirmed by peptide sequence. We have also demonstrated that the polB sequence is lacking in some strains. We conclude that DNA polymerase II is not a required protein in the cell. Sequence comparisons show that DNA polymerase II is an alpha-like DNA polymerase.