Folate polyglutamates in T4D bacteriophage and T4D-infected Escherichia coli

The folate compound which is a structural component of the Escherichia coli T-even bacteriophage baseplates, has been identified as the hexaglutamyl form of folic acid using a new chromatographic procedure (Baugh, C.M., Braverman, E. and Nair, M.G. (1974) Biochemistry 13, 4952-4957). It has also been found that the host cell contains a variety of polyglutamyl forms of folic acid. The major form is the triglutamate (about 50%) but small amounts of higher molecular weight folates including the octaglutamate (1.8%) have been identified. Upon infection with wild-type T4D bacteriophage there is a shift in the distribution of the folate compounds so that the folyl polyglutamyl compounds having the higher molecular weights are increased. Infection of E. coli with baseplate mutants of T4D containing an amber mutation in gene 28 resulted in the formation of significant amounts (over 7%) of folate compound(s) of molecular weight much higher than those observed either in uninfected cells or cells infected with wild-type T4D. It is suggested that the T4D gene 28 product functions to cleave glutamate residues from high molecular weight folyl polyglutamates to increase the availability of the folyl hexaglutamate for virus assembly.