Observations of interrelationships among T-even phages:

T4-like phages, with very complex tail structures and hydroxymethylcytosine replacing cytosine in their DNA, have been isolated all over the world. Studies in various labs using PCR, sequencing and/or hetroduplex mapping, seem to show that a large fraction of their genes are conserved. However, these phages show substantial insertions and deletions in a number of regions, and closer investigation of specific sequences often reveals more complex relationships. Here, we take advantage of the availability of the many phages of the T-even family and powerful PCR and genomic sequencing techniques to look carefully at one small region of the T-even genome--between gene 32, encoding the single-stranded DNA binding protein, and frd, dihydrofolate reductase.

Detailed examination of the sequence between gene 32 and frd, has been carried out, beginning with the classical rho-independent terminator after gene 32. Next lies the strong early promoter for a long transcription unit. Just down stream from the promoter lie at least three new uncharacterized ORFs of unknown function, frd.3 - frd.1. They are in a position generally indicative of a role in the transition from host to phage metabolism.

The sequence analyses presented indicate that the relationships among the various T-even phages are more complex and interesting than simply the shuffling of a few modules in heterogeneous regions. The analysis of frd.2 emphasizes that there may be a lot of genetic exchange among phages within apparent "modules" as well as between them.

Return to top.