The regA gene product of bacteriophage T4 is an autogenously controlled translational regulatory protein that plays a role In differential inhibition (translational repression) of a subpopulation of T4-encoded "early" mRNA species. The structural gene for this polypeptide maps within a cluster of phage DNA replication genes, (genes 45-44-62-regA-43-42), all but one of which (gene 43) are under regA-mediated translational control. We have cloned the T4 regA gene, determined its nucleotide sequence, and identified the amino-terminal residues of a plasmid-encoded, hyperproduced regA protein. The results suggest that the T4 regA gene product is a 122 amino acid polypeptide that is mildly basic and hydrophilic in character; these features are consistent with known properties of protein derived from T4-infected cells. Computer-assisted analyses of the nucleotide sequences of the regA gene and its three upstream neighbors (genes 45, 44, and 62) suggest the existence of three translational initiation units in this four-gene cluster; one for gene 45, one for genes 44, 62 and regA, and one that serves only the regA gene. The analyses also suggest that the gene 447-62 translational unit harbors a stable RNA structure that obligates translational coupling of these two genes.