Bacteriophage T4 mutants deficient in alteration and modification of the Escherichia coli RNA polymerase

An extensive screening of coliphage T4 mutants has revealed two distinct classes defective, respectively, in the two sequential phage-induced phosphorylations of the host RNA polymerase, alteration and modification. The existence of these mutants proves that T4-specified functions are involved in both processes. The viabilities of these mutants demonstrate that neither alteration nor modification is essential for growth in Escherichia coli B/r. Physiological studies after infection of E. coli B/r have failed to reveal any abnormalities of phage deficient in alteration or modification. Both mutants normally inhibit host protein and stable RNA synthesis and normally express all classes of T4 genes. Thus, these specific phage-induced structural changes in the host RNA polymerase are not fundamental to the control of gene expression during T4 development. Alteration and modification may be required for growth in some strains of E. coli and hence be selectively advantageous because they extend the normal host range of the phage.Alteration appears to be catalyzed by a T4 function injected with the DNA. A polypeptide of molecular weight 61,000, which is probably cleaved during morphogenesis from a precursor of molecular weight 79,000, is missing in phage particles of alteration-deficient strains and may be the phage activity so injected. The T4 gene involved in alteration is named alt.Modification is controlled by a T4-replicative gene that has been mapped into a region of about 500 base-pairs between genes 39 and 56. These mapping data show that the defect in α modification defines a new T4 gene, named mod.