Studies on the morphopoiesis of the head of T-even phage: IX. τ-Particles: Their morphology, kinetics of appearance and possible precursor function

Abstract

The τ-particles produced by bacteriophage T4 mutants in gene 21 or 24 are morphologically similar. Functionally, however, they are different. Particle counts in electron micrographs obtained from in situ lysed cells show that the number of τ-particles produced by a temperature-sensitive mutant in gene 24 decreases after temperature shift, whereas the number produced by a mutant in gene 21 remains constant after shift. Also, sucrose gradient centrifugation of lysates from pulse-labeled cells infected with a mutant in gene 24 shows that after shift to the permissive temperature, 50% of the radioactivity, when compared to wild-type, or 33% of the total label on the sucrose gradient migrates into a position corresponding to that of intact phage particles. Such a transfer of label is not observed in the corresponding experiment with a mutant in gene 21. Finally, gel electrophoretic analysis in the presence of sodium dodecyl sulfate (SDS) shows for mutants in gene 24 that about 50% of the major head protein, P23, and the phage specific proteins P22 and IP III are modified after temperature shift in a similar way as during infection with wild-type phage. Such modifications do not occur to a comparable extent with mutants in gene 21. Based on these results it is postulated that τ-particles produced by 24 − mutants can serve as precursors to mature phage heads if the functional gene 24 product is supplied. τ-Particles produced by 21 − mutants, on the other hand, are abortive.