Terminal proteins and short inverted terminal repeats of the small Bacillus bacteriophage genomes

Abstract

The genome of Bacillus phage phi 29 contains covalently linked protein at both ends. These DNA terminal proteins are essential for phi 29 DNA replication. We have isolated phi 29 terminal protein from each end separately and compared their two-dimensional peptide maps. Our results showed the two proteins to be identical. The DNAs of four phages examined (phi 15, Nf, M2Y, and GA-1) also contain protein at both ends of the DNA molecules. The chymotryptic peptide maps of these DNA terminal proteins have been compared with the map of the phi 29 terminal protein. Despite the similarities in molecular size, peptide maps of the terminal proteins show clear differences among the unrelated phages. These results are consistent with the idea that the terminal proteins are encoded by viral DNA rather than by the host chromosome. We have also determined the nucleotide sequences of the termini of four phage DNAs and compared them with the sequence of phi 29 DNA. The sequence data indicate that all of these phages DNA contain short inverted terminal repeats: 5'A-A-A-G-T-A for phi 29 and phi 15, 5' A-A-A-G-T-A-A-G for Nf and M2Y, and 5' A-A-A-T-A-G-A for GA-1.