AN ESCHERICHIA-COLI GENE (YAEO) SUPPRESSES TEMPERATURE-SENSITIVE MUTATIONS IN ESSENTIAL GENES BY MODULATING RHO-DEPENDENT TRANSCRIPTION TERMINATION

An extragenic multicopy suppressor of the cell division inhibition cau sed by a MalE-MinE fusion protein in Escherichia coli has been mapped and identified as yaeO, one of the two short open reading frames (ORFs ) of an operon located at 4.6 min. Overexpressed yaeO also suppressed some temperature-sensitive mutations in division genes ftsA and ftsQ, in chaperone gene groEL and in co-chaperone gene grpE. Gene yaeO, whos e expression is regulated by growth rate, codes for a 9 kDa acidic pro tein with no obvious resemblance to other proteins. Transcription term ination protein Rho co-purified with a histidine-tagged derivative of YaeO protein on Ni2+-NTA agarose columns in a manner that suggested di rect YaeO-Rho interaction. In vivo, yaeO expression reduced terminatio n at rho-dependent bacteriophage terminator t(L1) and at the terminato r of autogenously regulated gene rho, The suppression of temperature-s ensitive phenotypes was a consequence of anti-termination, as it could be mimicked by a P-rho::Tn10 mutation that reduces the expression and activity of gene rho. Our data indicate that the suppression is not c aused by overexpression of the mutated genes, but presumably by indire ct stabilization of the mutated proteins.