The article presents the nucleotide sequence of the rightward operator (O_R) of bacteriophage λ, determined using simple and rapid methods for direct DNA sequencing. The O_R consists of 74 base pairs and is recognized by the λ repressor. The methods described are applicable to sequencing DNA fragments with unique 5' ends up to 50 base pairs in length. The authors identify three repressor binding sites within the O_R. They also report a mutation in O_R that reduces its affinity for the repressor. The sequence analysis involves the use of restriction enzymes, end labeling, and partial nuclease digestion to determine the sequence of the O_R. The findings support a model for repressor recognition based on the sequences in both O_R and the leftward operator (O_L).The article presents the nucleotide sequence of the rightward operator (O_R) of bacteriophage λ, determined using simple and rapid methods for direct DNA sequencing. The O_R consists of 74 base pairs and is recognized by the λ repressor. The methods described are applicable to sequencing DNA fragments with unique 5' ends up to 50 base pairs in length. The authors identify three repressor binding sites within the O_R. They also report a mutation in O_R that reduces its affinity for the repressor. The sequence analysis involves the use of restriction enzymes, end labeling, and partial nuclease digestion to determine the sequence of the O_R. The findings support a model for repressor recognition based on the sequences in both O_R and the leftward operator (O_L).