Structure of bacteriophage T4 genes 37 and 38

Abstract

The distal half of the bacteriophage T4 tail fiber interacts with the bacterial surface during adsorption. The specificity of this interaction is controlled by the largest polypeptide in this half fiber, P37. During assembly of the half fiber P37 interacts with P38. These two gene products are incompatible with the corresponding gene products from the related phage T2: T2 P37 does not interact with T4 P38 and T4 P37 does not interact with T2 P38. Thus P37 has two specific functions, interaction with P38 and interaction with the bacterial surface. Both functions differ in specificity between T2 and T4. We have compared genes 37 and 38 of T2 with the corresponding genes of T4 to determine in more detail how the genes have diverged. Crosses between T2 and T4 phage which are mutant in genes 37 and 38 divide gene 37 into four segments which show different frequencies of T2-T4 recombination. These crosses show that both functional specializations of P37, attachment to the bacterial surface and interaction with P38, are determined by a single segment at the carboxyl end of P37. In this segment of gene 37 and in all of gene 38 there is no recombination between T2 and T4. The rest of gene 37 contains a segment with a small amount of T2-T4 recombination flanked by two small segments with relatively high T2-T4 recombination. When T2/T4 heteroduplex DNA molecules are examined under the electron microscope, four heterologous loops appear in the region of genes 37 and 38. When genes 37 and 38 are aligned with this heteroduplex pattern, regions of low recombination correspond to regions of T2-T4 heterology. Begions with relatively high recombination are homologous. As determined from sodium dodecyl sulfate polyacrylamide gels, the molecular weight of T2 P37 is about 13,000 larger than that of T4 P37. Analysis of T2-T4 hybrid phage has shown that, like the functional differences, this molecular weight difference is determined by the carboxyl terminal segment of P37.