Autogenous regulation of the gene for transcription termination factor rho in Escherichia coli: localization and function of its attenuators

Abstract

We present evidence that the expression of rho is regulated by rho-dependent attenuation of transcription. Gene fusion analysis with nested series of deletions of rho indicated that the transcription of rho is attenuated in a rho-dependent manner in the leader region and that neither a read-through transcription from the upstream gene, trxA, nor a modulation of transcription initiation of the rho promoter is involved in the self-control of rho. Si mapping and Northern hybridization analyses localized at least six transcription attenuation or termination sites in the region ranging from the 3' end of the trxA structural gene to the middle of the rho structural gene. Among them, the most upstream site overlapping the rho promoter sequence was assigned to the terminator for the trxA gene, and the second and third sites, mapping about 80 and 50 nucleotides upstream from the start codon of rho, were suggested to function as the major attenuation sites for regulation of the rho expression. Further, the start points of the trxA and rho RNAs were determined in an in vitro transcription system to be located 111 nucleotides (U) and 255 nucleotides (G) Kushner, Gene 32:399408, 1984).The termination of transcription plays profound roles in the regulation of gene expression in procaryotes. Termination of RNA synthesis generally occurs at the ends of operons so as to ensure independent expression of neighboring genes. In addition, it can also occur within operons to allow differential expression of genes within an operon. In Escherichia coli, several protein factors which participate in transcription termination or antitermination have been identified: Rho, NusA, NusB, and NusE (14,21,22,25,26,30,47,56).Rho protein causes termination of transcription catalyzed by E. coli RNA polymerase at certain specific sites on DNA template (47). These sites are called Rho-dependent terminators, as opposed to Rho-independent terminators which are recognized by RNA polymerase without the aid of Rho. Several Rho-dependent terminators have been found at different positions in various operons. For example, trp-t' (57) and the tyrT terminator (33) are located at the ends of their operons, while tLl, tRl, and tR2 are within the leftward and rightward operons of bacteriophage X, respectively (47). It has also been shown that mutational polarity involves Rho-dependent terminators residitng within a structural gene.Such terminators are normally nonfunctional, but are activated when preceding translation is arrested at a nonsense codon introduced by mutation (1, 13). A number of rho mutants of E. coli have been isolated that are defective in Rho-dependent transcription termination (12,28,29,31,46). Some of them are conditional-lethal, suggesting that Rho is essential for cell growth. (27, 45). Conversely, decreased Rho levels have been observed with a new class of rho mutants which is hyperactive in termination (53). These observations suggest that the expression of rho is autogenously regulated. In view of the role of Rho as a transcription term...

Dual-acting riboswitch control of translation initiation and mRNA decay

“…In contrast, we observed that bicyclomycin had a strong effect on the level of rho mRNA (SI Appendix, Fig. S5), which is known to be autoregulated via a Rho-dependent mechanism (20). Therefore, our results show that the level of the lysC mRNA is not controlled via a Rho-dependent transcription regulation mechanism.…”

Identification of a Salmonella typhimurium invasion locus by selection for hyperinvasive mutants.

“…Results of previous studies suggest that expression of Salmonella adherence and invasion factors is induced by the low oxygen environment of the intestinal lumen (13)(14)(15) obtain rare transposon mutations that affect the expression of rho, an essential bacterial gene, by insertion in the 300 base pairs that comprise the promoter of rho (28,31). Only three genetic loci were identified that result in increased aerobic invasiveness.…”

An Escherichia coli gene (yaeO ) suppresses temperature‐sensitive mutations in essential genes by modulating Rho‐dependent transcription termination

“…In view of the binding of YaeO to Rho, the requirement for a strong expression is not surprising as Rho is abundant (approximately 0.3% of total proteins), and autoregulation of rho (Blumenthal et al, 1976;Brown et al, 1982;Matsumoto et al, 1986), as illustrated in Fig. 5, may further dampen the effects of YaeO.…”

“…was analysed. It is known that the rho gene is autoregulated by termination in the leader region of the gene by t rho (Brown et al, 1982;Tsurushita et al, 1984;Matsumoto et al, 1986). We tested the inhibition of Rho function by measuring the expression of gene rho in a pSC101-derived plasmid in which most of the rho coding region was replaced by lacZ (Fig.…”

“…Partially defective rho mutants have markedly increased levels of the protein, while hyperactive mutants have lower than normal levels (Imai and Shigesada, 1978;Tsurushita et al, 1984). Studies of the rho promoter region have revealed that rho-dependent termination approaching 90% occurs at two sites within the long 5Ј untranslated region (Brown et al, 1982;Matsumoto et al, 1986). Autogenous regulation of rho provides a mechanism whereby Rho activity can be adjusted rapidly to its normal level after a transient perturbation.…”