Bacteriophage λ PaPa : Not the Mother of All λ Phages

Abstract
The common laboratory strain of bacteriophage λ—λ wild type or λ PaPa —carries a frameshift mutation relative to Ur-λ, the original isolate. The Ur-λ virions have thin, jointed tail fibers that are absent from λ wild type. Two novel proteins of Ur-λ constitute the fibers: the product of stf , the gene that is disrupted in λ wild type by the frameshift mutation, and the product of gene tfa , a protein that is implicated in facilitating tail fiber assembly. Relative to λ wild type, Ur-λ has expanded receptor specificity and adsorbs to Escherichia coli cells more rapidly.