A temperature sensitive mutant of Escherichia coli which does not allow replication of RNA phage at a high temperature.

A conditional mutant, referred to as RepR43, was isolated from Escherichia coli W2252 by N-methyl-N'-nitro-N-nitroso-guanidine mutagenesis. Although RepR43 does not permit growth of RNA phage beta at the restrictive temperature, 43 degrees C, cell growth and synthesis of macromolecules such as RNA and protein continue at a somewhat reduced rate. Several lines of evidence indicate that a RepR43 function is indispensable for normal phage RNA replication. In addition, this function appears to be involved in the maintenance of the perpetuated phage genome. The addition of 10% sucrose to the medium at the restrictive temperature resulted in the production of the phage, suggesting that the mutant cell might have an altered membrane organization which interferes with normal viral replication.