Abstract
Polypeptides of low mol. wt. have been extracted from T4 coliphages and from Escherichia coli B cells infected with a wild type and various amber mutants of bacteriophage T4. Six peptides were fractionated by chromatography on phosphocellulose: three of them were cleaved from proteins synthesized late in infection and related to phage head. The remaining three peptides have been shown to arise from early-labelled phage-induced proteins. Two of these six small petide fragments were found in the head of the T4 phage.