[Reversion of RNA-polymerase mutations affecting F'-factor stability].

Ts+ reversions of amber mutations tsR on the beta-subunit of Escherichia coli RNA polymerase (79 min on the genetic map) were investigated. TsR mutants are viable due to the partial suppression of amber mutations by su2 suppressor. Three types of reversions were isolated in the course of the selection for Ts+ character, namely, intragenic reversions and two types of extragenic reversions, located at different regions of the bacterial chromosome. The mutation N5, located between 0 and 15 min. on the map, increases practically to normal the amount of RNA polymerase beta-polypeptide, which is diminished as a result of ts22 amber mutation action, and increases the plating efficiency of several T4 phage amber mutants. The mutations designated as D are located on the chromosome near the spcA locus (64 min. on the E. coli map). These mutations are characterized by pleiotropic effect. They have properties of a weak suppressor increasing the efficiency of su2 action on amber mutations of E. coli and phage T4. At the same time D mutations are capable to decrease sharply the efficiency of the crosses with F' strains. Both these characters determined by D mutations do not segregate in transduction. It is suggested that the decrease of sexduction by D mutations depends on their influence on replication of episomes in the recipient cells.