DNA sequence of tail fiber genes of coliphage 186 and evidence for a common ancestor shared by dsDNA phage fiber genes.

We present here the nucleotide sequence of the tail fiber genes of phage 186. Marker rescue was used to associate an open reading frame (ORF) of 462 codons with the previously known tail gene K. A downstream ORF, encoding a 166-amino-acid product, was designated orf 45. Comparative studies suggested that K encodes the tail fiber protein and that orf 45 encodes an assembly protein. K protein contains a succession of short amino acid sequences (motifs) that are homologous with sequences from the tail fiber proteins of unrelated bacteriophages. The fact that these sequence motifs are variously present in the tail fiber proteins of unrelated bacteriophages has been advanced as evidence for horizontal transfer in the evolution of the associated tail fiber genes. However, the fact that the order of the various motifs in the proteins is invariant emphasizes the probability that independent divergence from a common ancestor also played a major role in the evolution of the tail fiber genes.