Characterization of the bacteriophage P4 sid⁺ derivative overcoming P2sir-associated helper inefficiency through DNA conformational adaptation

Abstract

A certain size of DNA (28-29 kb long) to be packaged into P2-size head and the mutation in sid gene of bacteriophage P4 are the major factors to overcome "P2 sir-associated helper inefficiency". To clarify whether the presence of sid mutation is essential to overcome "P2 sir-associated helper inefficiency" or not, we tested the P4 derivative, P4 delRI::kmr, which is sid + and whose genome size supposed to be 28.5 kb long in the case of being packaged into P2sir3-sized large head. As P4 delRI::kmr showed the low EOP with P2 sir3 lysogen, P4 delRI::kmr phage stock was prepared in P2 sir3 lysogen host to increase the EOP with P2 sir3 lysogen. Through this process, P4 delRI::kmr had been adapted for P2 sir3 lysogen. With a CsCl buoyant equilibrium density gradient experiment and gel electrophoresis of the isolated DNA, it was evident that the adaptation of P4 delRI::kmr for P2 sir3 lysogen was caused by the conformational change of DNA to be packaged into large head. The burst size determination experiments with P4 delRI::kmr phage stock adapted for P2 sir3 lysogen and normal P4 delRI::kmr phage stock showed that not the sid mutation but the size of DNA to be packaged (28-29 kb long) was essential to overcome "P2 sir-associated helper inefficiency".