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Bacteriophage lambda PaPa: not the mother of all lambda phages.

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