Host factor requirements and some properties of phiXtB. An evolutionary aspect of phiX-type phages.

Replication of phiXtB, a capsid mutant of bacteriophage phiX174, depends on the host functions directed by the E.coli genes dnaE, dnaF, dnaG, dnaZ, lig and rep. The cellular products of dnaA, dnaB, dnaC(D), dnaI, dnaP, polA, polB and xth genes are, however, dispensable for the viral growth. In these host factor requirements, phiXtB resembles phages phiK and St-1 rather than phiX174. Host ranges of phiXtB, St-1 and phiK overlap considerably, and growth temperature of the three phages is somewhat higher than that of phiX174. Furthermore, phiXtB is, like phiK, inactivated by antiserum against St-1. phiXtB may thus fill an evolutionary gap between the phiX174 group and the St-1 group.