Gene rIII is the nearest downstream neighbour of bacteriophage T4 gene 31.

The nucleotide sequence of the 2218-bp T4 DNA fragment encompassing gene 31 and five complete open reading frames (ORFs) is presented. We show here that one of these ORFs, ORF31.-1, located downstream from gene 31, is the rIII gene. The position of the gene was established by comparison with the sequences of the rIII gene mutants, r67, rES40 and rBB9. The ORF corresponding to the rIII gene encodes a basic protein of 82 amino acids with an M(r) of 9323 and a pI of 9.28. According to the Chou and Fasman [Adv. Enzymol. 47 (1978) 45-148] secondary structure prediction, the rIII protein has a relatively high helical content. In addition, discrepancies with the overlapping sequences determined by other authors in this region are indicated.