Mass distribution of a probable tail-length-determining protein in bacteriophage T4

Analysis of dark-field scanning transmission electron micrographs of unstained freeze-dried specimens established that the interior of the intact bacteriophage T4 tail tube contains extra density that is missing in tubes artificially emptied by treatment with 3 M guanidine hydrochloride. The mass of the tail tube is 3.1 X 10(6) daltons, and the central channel is 3.2 nm in diameter. Quantitative analysis of the density data is consistent with the presence of up to six strands of a protein molecule in the central channel that could serve as the template or ruler structure that determines the length of the bacteriophage tail and that could be injected into the cell with the phage DNA.