Alteration of Escherichia coli RNase D by infection with bacteriophage T4

Infection of a variety of E. coli strains with bacteriophage T4 leads to about a 25,000 dalton increase in the apparent molecular weight of RNase D based on gel filtration on Ultrogel AcA44. No alteration occurs when infection is carried out in the presence of chloramphenicol. The change in RNase D is substantially completed by 7.5 min of infection. Chromatography of the altered RNase D on the adsorbant, Affi-gel Blue, restores the enzyme to its original molecular weight of 40,000, indicating that the modification is reversible. Mixing an extract from infected cells with one from uninfected cells converts a portion of the uninfected cell enzyme to the higher molecular weight form. No conversion takes place if the infected cell extract is first treated with phenol to inactivate proteins. Preliminary analysis indicates that the factor in infected cell extracts responsible for the conversion is a heat-labile, relatively low-molecular weight protein, and that RNase D is modified by association with this phage-specific component. The potential role of RNase D in the 3′ processing of bacteriophage T4 tRNA precursors, and the involvement of a phage gene product in this process, are discussed.