Diagram relating the phage T5 physical and genetic map. The double-stranded DNA duplex (black lines) consists of one continuous (upper) and one nicked strand. Pre-early genes are encoded on the terminal repeats (dark shaded). The early and late regions are shown in white and grey, respectively. Genes coded on the top and bottom strands are shown above and below the bars respectively. Black arrows and a diamond show the positions of viable deletions.